I've just got a 50g one. It's a really nice rug - I've not used the belly guard yet but the only issue I have with it is the velcro at the front is a bit crappy so it folds.
No. If anything they are a little bit big in the belly. Brilliant rugs, I have the 50g with neck for my mud monster and it does a fantastic job of keeping him dry and comfy (and mud free!) all through the winter. I would say they're well worth the money, particularly if you can get one on offer. I bought mine and another livery liked it so much she bought one too.