Pigloos are great for a lot of guinea pigs, however, please be aware that the ventilation inside can be somewhat limited.
NOTE: Do not use custom fleece covers over the pigloos.
They may look cute, but they are not appropriate for health and safety of most guinea pigs. However, for skinny's you may find that it provides more warmth.
If you have male guinea pigs it's probably best to avoid using pigloos, as the confined entrance to the pigloo can cause males to become territorial.
You can avoid scuffles by using more male-friendly hideys such as the "Critter Hollow"