Firstly you need to differentiate between the two types of printer Riso make. There are duplicators and inkjet models, both very different. I think some people here are mixing the two up. The duplicators use a drum and master, and are OK for printing a few thousand of the same image - not suitable for the intended use here as they cannot do any collation. I've currently got one knocking out 20,000 black and white cheap leaflets. Not the best quality, but OK as long as you accept its cheap and cheerful printing and sell it as that.
They then do inkjet models, such as the ComColor machines. We also have one of those, and again you have to accept the quality is not perfect, it's quite acceptable for text only work, and even some images come out OK. We use ours for church newsletters, ncr's, forms, etc, and its very fast, cheap to run and outputs collated blocks ready for offline binding. So long as you have the right expectation, they're a useful addition. The biggest drawback to all Riso machines, it that they cannot print on coated stocks.