I notice that nobody has yet answered your post so I thought I'd do some investigating on your behalf. I only found one site which posted about individual problems with Uro-leg bags and they seemed to be about the type of activity which tends to pull at the system( Motorbike riding).
Most of the major manufacturers supply them and they are only a few dollars. However, I have found that companies like Coloplast are very good at supplying free samples and they have an advice system whom you can contact for a discussion about your needs.
The only direct knowledge I have of the system is from my clients. some have bags on the top of their legs near their stomas and others have had bags on their ankles. The ankle ones are so much easier for the likes of 'carers' to empty as they do not involve any undressing. However, it can involve having to bend the leg up to rest on the toilet edge, which is not always possible or safe for the elderly and frail. Of course, these type are ideal if there is somewhere at ground floor level to empty them (like outdoors or into a container). Unfortunately, there is still a problem for those who cannot bend to reach the bag as they cannot do this for themselves.
Some use a bag that is strapped to the top of the leg but I cannot see very much advantage to these, as the wearer still has to undo clothing to gain access, so it would appear that a straightforward stoma bag would do the same job.
I don't know if this post is of any help but I do suggest that you contact the manufacturers for advice and samples.
Alternatively you could have a chat with a stoma nurse or the bowel and bladder department of you local health region.