I have! My guinea-pigs are very happy in it (as far as you can tell with guinea pigs!) We kept them in it all last winter and unless it was pouring with rain they would come out in the run and forage every day. I did buy some of the those heat pads to put under their bedding for the cold days and nights, and a little mini-igloo thing so they could be really snug. They take it in turns to snuggle up in the hay rack when it's cold. In the long evenings now they are out in the run all the time.
It is very heavy and, though easy to clean coz it's plastic, I find getting the top off quite cumbersome/tricky. They eat the grass incredibly quickly too so you have to move it every day or so. The bedding also falls out of the front of the Eglu when they run in and out.