They've got their uses - two together make good trestles, and the single small one I've got is a competent SCMS stand (SCMS bolted down tightly!). The larger two I've got are very useful indeed.
The late and much missed Niki (of this forum) used to use one similar to mine as a router table, and I've done the same in the past -- it works really well with a gash bit of melamine-faced chipboard as the surface (plunge the router through once you've fixed it on).
That said, I think it's wise to replace the nuts provided with Nyloc ones (the anti-shake washers are pretty useless), and possibly put diagonal bracing on the framework. But given the cheapness, they're really useful.
E.