I love fleece and have been using it for years.
I started out with fleece and puppy pads, but that cost way to much for my liking. So I switched to Fleece and towels, which I used for many years. In August I switched out to Fleece and Uhaul pads. I LOVE them. There is little to no smell and they soak up the pee very well.
Some things you should know about using fleece with guinea pigs. You will have to sweep their poops daily or more. I clean mine two times a day, once in the morning and once at night. Washing Fleece bedding can be a pain, you do have to make sure there is nothing on the fleece, no poops or hay. These can clog your washer, though I have never personally had this issue. A good brushing can get rid of this issue.
Another thing you should know is depending on the size of the cage you may have to clean out the cage 1-3 times a week. This is a complete cage. My cages are 2x5 housing 2 guinea pigs each. I clean 2-3 times a week. I do this not only for my pigs but for my kids as well, flung guinea pig poop sitting on the floor is very tempting for a toddler. But the good thing about cleaning so often is its all washable! Just wash and dry and your done. I have two sets for both my cages, this means I can wash one set and use the other.
All in all fleece is great, it gives them a soft area to walk on, helping and preventing bumblefoot and other health issues. It also allows you to see any urinary issues, like bladder slug which can cause stones. If they get a UTI, you can see the blood much more easily, even more so if you use white towels or light colored fleece.