(I am not a tech, just a mom with firsthand experience
)
We have had a True Fit for a little over a year now (we were one of the testers) and have installed and used it in three cars, an '05 Hyundai Elantra, an '08 Nissan Versa and an '08 Chevy Cobalt.
In my opinion the seat is fairly easy to install and use, but it has lots of quirks. It installs rear facing (we have never tried a forward facing install with it) like a dream in the Versa, and pretty easily in the Elantra, but was a nightmare to get correctly installed in the Chevy Cobalt. The biggest problem for me is making sure that the latch belt/ seatbelt do not interfere with closing the lockoff (and since the lockoffs must be used, even with LATCH or a locking retractor, this can be a real pain in some cars.)
Once installed rear facing, the biggest problem is that the harness adjuster is a pain to get to in the Versa, hard to get to in the Elantra and completely inaccessible in the Cobalt when the seat was at the 35 degree angle.
I have never had a Roundabout 50, but I did have a Marathon and it was very easy to install and use correctly. However, I really question that
any carseat can be easily and safely used without reading the manual.