I had one of my buns rearguarded at the vet's a few weeks ago. The vet recommended it because Toby sometimes gets a sticky bottom. However, having now done a lot more reading up on here and elsewhere, I don't think I will be having it done again, as I hadn't realised before that as soon as you wash their bottom, the rearguard is no longer active as it gets washed off (at least that is what I understood from what I read).
I am now trying to protect them just with other methods (keeping all areas clean, fly netting, citronella etc, and washing bottoms when necessary).
I'm not sure which product is best though if you do choose to get it done.