The Bumgenius All-in-one Hook & Loop is very similar to the Bumgenius One Size Hook & Loop. The materials, washing routine, and use are pretty much the same. The velcro has similar durability. I used the size medium with my daughter for 3 months. When I sold them used, they were in the same condition as when I bought them. Again, it's important to take care of them to keep them in great condition.
There's only two differences between the all-in-one (AIO) and the one size (OS). The AIO is a specific size and it has one microfiber insert sewn into the cover. The benefit to having a specific size is that it reduces the extra fabric and bulk on the baby. You also don't have to use snaps to adjust the fit. Having the microfiber insert sewn into the cover is convenient for those who don't like to stuff diapers. It also removes the necessity of reaching into a dirty cover to remove the inserts before washing. However, if your little one is a heavy wetter, you may need an extra liner in the diaper (which isn't included in the diaper when bought new) so you'd have to stuff the diaper anyway. Also, the sewn in liner means it takes a little longer to dry in the dryer.
Overall, I really liked the sized AIO diapers. They were very durable. They are trimmer than the OS diapers on smaller babies. It takes less time to get the diapers ready between dryer and baby's bum. I did find that due to only having one insert, they weren't as absorbent as I would have liked. I ended up changing our daughter more frequently than I like to because I wanted to avoid stuffing the diapers with an extra liner. It also requires a change in size as baby grows, which increases your cloth diapering cost.