My two play with theirs indoors and out. I thought it would only really go on hard surfaces but I've been surprised how well it copes with carpet. The castors are relatively easy to wipe clean if it gets muddy/wet outside. I'd vote for the wheelybug, the girls play with it loads, not just as a ride-on but it's often a dog or a dragon or whatever in their games too.
I think so yes, though it's easier for me to say as my mum bought ours! We also have a regular plasticy ride-on that wasn't much cheaper at £35, and it hasn't lasted nearly as well or been played with or loved half as much. In fact, I can't remember the last time I saw it. Wheely Bee has never been put away, even in the evening when we tidy all the kids stuff up so we have some grown up space we leave Bee out cos he's so cute.