We have the Britax Duo Isofix. We got itabout 1.5 years ago now and it has been fantastic. I would certainly recommend it for several reasons, and it is the best £150 we have spent really.
It is the safest car seat tested in the last set of tests.
It is incredibly easy and quick to fit using the Isofix fittings, and it doesn't budge once fitted. It is virtually impossible to not fit it properly - one of the biggest problems with other seats.
It can be fitted into a non-tested or non-Isofix car as you would do any other car seat, and it sit gets good safest records.
Have you been on the Britax website and checked that your car has been tested to be suitable for this car seat? Most have and it is updated often. If unsure, phone Britax. But not all Isofix cars are tested by Britax for this chair. For example Volvo's have Isofix buy the Britax Duo is not tested for use in it.
The car seat may be expensive when compared to other car seats but IMO worth every single penny. Safety was my biggest priotity when buying it, and still would be. Therefore this wins each time for me!
If you want to know any more, ask away!