Adjustable spanners struggle a bit with a bad reputation. Being seen using one is often accompanied with sucking of teeth from an "tool experts" looking on.
I get it - they are a compromise and using the specific size spanner is always a better choice. However, they have their place and I would always have one in a tool kit especially if in a vehicle.
Why? because for an emergency repair they are extremely useful. It saves me having to carry a full set of metric spanners. In the case of the Land Rover I'd need to carry both metric and imperial. A single adjustable spanner can sit there happily until being needed.
Quality is always important when it comes to tools, but especially so with an adjustable spanner. When they are bad, they are really bad. Loose jaws that don't hold position. Soft jaw material that is just waiting to round the nut that you are trying to sort out.
In my opinion Bahco make some of the best quality adjustable spanners. They should do really as they invented them over 130 years ago. The Swedish companys tools are still made in their own factories across Europe and where bought by Snap-On in 2005.
To mark their 130th anniversary they made this 8" adjustable spanner. It's a wide jaw model which means it can open up to 40mm.
The phosphate finish is extremely durable and provides a rust resistant finish.
If I didn't already have a Bahco adjustable spanner in each vehicle tool kit, this would be the one I'd be carrying.