It's not that it's a bad seat necessarily, it's just that there are many better options out there for the same amount of money.
The issues with that particular seat are:
1. Harness slot height - very low. Lower than pretty much all convertibles, let alone all other combination seats. Combine that with the 40 pound weight limit on the harness, and most kids will outgrow it long before they are ready for a belt positioning booster. Those kids who do still fit height wise may even be eligible to still rf.
2. difficult install - the few I have run across have been a real bear to install.
3. totally inadaquate as a booster - the belt guides are sewn to the cover, and do a very poor job for actually positioning the seat belt. They also will allow slack in the belt.
If it fits your child and you vehicle, it's a perfectly safe seat, but as I said before there are definitely better seats out there to be had for the same amount of money.