I personal feel this is 100% safe as per the Regulatory standards and comfortable for the toddler. You can get a Maxi Cosi cushion head support for side impacts as well. Easy to slide into isofix slots and snaps itself automatically in no time. Easy to clean. Elevated view for the toddler.
Downside - In my Audi A6, the isofix extension (the long metal rod) leaves its hard mark on the floor no matter what. It is very heavy to move it from rear to front seats and vice-versa.