Hey mate,
I have been using a roller for a few months now and I just love it. Can be relaxing or painful ( but the great pleasure type) we have a really good one here at work and seems to be comprised of a few pieces of fairly solid foam, stuck together. I am guessing the centre section is to provide some strength. Its quite firm, but still you can press it in with your grip. It also has some litele knobby bits on it. I am guessing its a pretty decent quality and costs about 50$. it gets used many times a day. by our employees.
Now.. At home I bought one a few weeks ago and it was "only" $30! BUT... when I got it home I noticed that it was definatley not as good as the one above I just mentioned. Its made from softer foam, ( one piece) its fairly soft too with a pretty boring texture. I have used it every day and in just 2 weeks it seems to have changed shape! Im not too happy.
So mate definately shop around and dont be in a hurry like I was! haha
after work to day Ill be back on th roller for sure. I have found using it when ever gets great releif but being technical I am not too sure of when would be the best time.
good luck.
Jase