Don't be worried.
We don't rent an
ecv since DD has her own wheelchair (I've been working on my FIL tto rent one for years, but that's another story).
Posters to the DIS boards generally rent from one of these 3 companies: Care, Walker and Randy's. Everyone has their favorite, but in general, you won't go wrong with any of them.
The one thing that is different about Randys is that you need to be physically there to have the ecv delivered to you. That is the only thing I have ever seen people complain about regarding Randys.
Some people would rather have the ecv waiting at their hotel when they arrive, but others find advantages to being there and having it delivered to you.
For one, you can get any questions or things about the ecv demonstrated to you rather than trying to explain or listen to an explanation over the phone.
The last time I checked, Randy's prices were a little less expensive. One of the reasons may be that (at least I assume) they may have lower insurance and/or repair bills because of their "deliver it to you" policy.