We installed ours ( flow rite) when we first bought our MH. Our battery tray doesn't slide out and the rear batteries ( 6 house) were almost impossible to service much less fill without making a complete mess.
This system has been a complete pleasure to use. It works as described. Takes me 5 minutes or less to service the batteries from standing outside the Battery bay.
The only problem we had on one extremely cold winter was the filler valve froze on one of the three making it inoperative. I ordered a few extra and replaced it with no problems.
When topping off in the late fall I now just push in on the valve releasing the pressure in the tube after filling. Solved the problem.
If you have problems getting to your batteries I would highly recommend this. Even if you have easy access to yours batteries it would make the top off task much faster and cleaner.