The GLB offers the same engine and powertrain combinations that you'll find in other compact Mercedes models. This means that the starting point to the range is provided by the same Renault-derived 1.3 litre petrol turbo engine you'll find in an A-Class. In the GLB 200, it puts out 163hp and drives the front wheels through a 7-speed dual-clutch auto gearbox. If you want the option of 4MATIC 4WD, you'll need to move to a diesel, the 150hp GLB 200d. In the next model up, the GLB 220d with 190hp, you have to have the 4MATIC system, a variant that can be specified with an optional off-road engineering package. This gives you hill start and descent assistance, LED Multibeam headlights and an extra off-road driving mode which includes a special infotainment display showing gradient, technical settings and your various incline angles.
At the top of the range sits the Mercedes-AMG GLB 35 performance model, which gets the 306hp 2.0-litre turbo petrol unit from the A 35 hot hatch. Power comes through an 8-speed dual-clutch auto gearbox with a race start function. Plus there's an AMG Dynamic Select driving modes system that as well as the three modes featured in other GLBs ('Comfort', 'Sport' and 'Individual') also features two further ones ('Slippery' and 'Sport+').
The look of the GLB draws inspiration from Mercedes' grand 'G-Class' 'Gelandewagen' - which you need to know because otherwise, you might wonder why it's quite so squarical and van-like. Even Designer Robert Lesnik describes it as 'a box with rounded edges'. The dimensions are a little confusing too, this car actually being almost the same size as the GLC model it supposedly sits beneath in the Mercedes SUV line-up; this GLB's 4.63m length sees it measuring in only 21mm shorter than a GLC - and it's actually 18mm taller than that car.
Inside buyers get much the same 'widescreen cockpit' instrument layout as you'll find on all the company's modern compact models. And as usual, it's controlled by the brand's MBUX voice-activated interface. All this hardware integrates into a rather unusually shaped dashboard, this one with an aluminium-look 'tubular' lower element. In the second row, the boxy shape contributes towards quite a spacious feel. And if you're going for a GLB with 7 seats, you'll get an easy-entry feature to reach them. As for the boot space, well there's 560-litres of it in the 5-seat model, which to give you some perspective is 140-litres more than you'd get in an Audi Q5. And you can expand that by flattening the 40:20:40-split backrest to free up 1,755-litres. In 7-seat GLBs, the third row pews fold flat into the floor when not in use.
Pricing starts at around £34,000 and there are four trim levels - 'Sport', 'AMG Line', 'AMG Line Premium' and 'AMG Line Premium Plus', with prices in the mainstream range rising up to around £46,000. Generally, you have to have seven seats, though Mercedes does offer a single five-seat GLB 220d 4MATIC model with mid-range 'AMG Line Premium' trim and a price tag of around £42,000. Think in terms of over £50,000 for the top high performance Mercedes-AMG GLB 35 4MATIC variant.
All mainstream models are well equipped. Even entry-level 'Sport' variants come as standard with 18-inch five-spoke alloy wheels, the 'Dynamic Select' driving mode system and LED headlights and tail lights. Plus across the range you get a 180-degree reversing camera, aluminium roof rails, two-zone Thermotronic climate control, heated front seats and Artico man-made leather upholstery. Infotainment includes a DAB tuner, a six-speaker/100 watt sound system, a seven-inch digital cockpit display and seven-inch touchscreen media display, the MBUX multimedia system and 'Hey Mercedes' voice activation. Plus you get Mercedes me connect (which includes emergency call system (eCall), accident recovery, breakdown management and maintenance management).
Standard safety and assistance equipment includes Active Brake Assist, Active bonnet, Active Lane Keeping Assist, Attention Assist, Speed Limit Assist, and Keyless-Go locking and unlocking.
The engines used here deliver decent returns in other Mercedes compact models, so we'd expected the same from the GLB - which is broadly how it turns out. The base petrol GLB 200 manages a 47.1mpg WLTP-rated combined cycle reading, plus a 138g/km NEDC-rated CO2 emissions reading. For the GLB 200d diesel, the figures are up to 56.5mpg and 133g/km in 2WD form, or up to 51.4mpg and 145g/km as a 4MATIC. The GLB 220d 4MATIC diesel manages 51.4mpg and 146g/km of CO2.
As you'd expect, the Mercedes after-care package is comprehensive, with a three-year unlimited mileage warranty that's matches BMW. This is built upon by Mercedes' Mobilo scheme which delivers breakdown cover for up to thirty years, as long as you continue to have your car serviced at a Mercedes main dealer. Ah yes, maintenance. As usual with one of the Stuttgart brand's models, there's an ASSYST PLUS dashboard service indicator that monitors engine use and tells you exactly when a garage visit is due. Fixed price servicing is available across the range and most buyers opt for the Mercedes ServiceCare plan that could cost you as little as about £28 a month based either on a two-service/two year deal, three years with three services or four years with four services.
At first glance, you might think the GLB an unnecessary further addition to the Mercedes SUV line-up. After looking closely at what it has to offer, we've ended up concluding that going forward, it's likely to be a vital part of it. The brand has never before offered a car in this class that's really practical for a growing family, yet remains reasonably affordable. This is it.
Are there issues? Well probably, you could pay slightly less and get a slightly bigger seven-seat SUV in this class from a volume brand but after trying a GLB, we think you may not want to. It has a premium, desirable feel that cars like SEAT's Tarraco, Skoda's Kodiaq, Hyundai's Santa Fe and even Volkswagen's Tiguan Allspace struggle to match. And the interior technology of those cars seems rather yesteryear compared to the cabin media tech on offer here. You probably won't have started off wanting a GLB in this class. But take a look at one and, if you're prepared to pay a slight premium, you could find it a difficult package to overlook.