I have a fill system on one of my carts. This cart is a 2002 CC and has 8 batteries and it would be almost impossible for me to fill two of the batteries. I periodically pull caps off to check levels and have never seen an issue.
Until this thread I had never heard of a an issue where the float stuck closed so the battery would not fill (That is very scary and harder to notice I bet). I have heard stories of the float sticking 'open' and folks overfill without noticing water coming out top of battery as they fill.
My other cart is a 2002 CC with 6-8v batteries. I find it simple to refill pack using a turkey baster. Hint: Make sure you buy a new baster. If your lovely wife is cooking and cannot find a baster and you bring it in from the garage, explaining it is only distilled water will not help your case...
In summary, it is just one more moving part I have to check/maintain and I will likely only have one if filling the batteries was difficult as with my first cart.