We use the real stuff from Norland all the time for optics. I've never used the cheap stuff, but conceptually it's all the same, and very useful to be able to place, partially cure, tweak, cure a bit more, and then do a full cure. Some of the Norland stuff also has a heat catalyst, so you can use UV for an initial tack and then oven cure to ensure that even adhesive between opaque objects gets cured.