The vault-tec one will probably be worth getting, I know some are saying its not, but some also said automatron would be worthless, and it turns it was actually pretty damn cool. You know, just saying. Anyway as for contraptions, well its really up to you. The useful thing about it is that you can build your own weapons and armor, not very useful if you've already beat the game and are a high level, buuuut if you start a new game in particular on survival mode, it can give you an edge in the form of constructing say a gauss rifle, ammunition for it, and a full set of heavy combat armor. There's even a mod which further enhances the dlc by making it so the resource getting machine (what? I forgot its name...) uses resources from all linked settlements and doesn't have to be by the workshop bench, and also adds new builders that allow for building power armor parts. Think about that, level 15 and already a full suit of T-60, or X-01 you know, which ever so you like best. So, useful right? The real question though, is it worth the $5 it'll cost? Get some real information on it, watch some gameplay vids of it, and decide for yourself whether or not its worth it.