Their design and and fit is biased towards the rear, but I didn't have any side-leaks whilst experimenting with them.
They've been compared to ye olde Comficare, but I think that Comficare would be a better option for sidesleeping (were they still available).
(Both products tried as Large size on a 13-14 year old sized frame).
I find Forsite one of the best diapers available period. I use these mostly for overnight as I do find them better than most diapers for side sleeping which I mostly do. I have had the occasional leak in them but it is rare and the medium size wrap around me pretty good if put it on nice and tight.
I use them for nighttime and they are really good but for me require a booster like most night diapers.
In Europe they're priced at 19.9 eur for a pack of 10 which is a lot, given the fact I can manage just as well with a forma care xplus + booster which is much cheaper.
I do think that this price is due to import so if you're Canadian they're definitely a good choice.
When the rear is soaked I did leak while sitting on the side of my bed though... Plastic pants is recommended if you're a heavy wetter.