Shower Valve Inst - Male Threaded fittings or Unions?

Is it a good idea to use unions to attach a shower valve?

In the past, I have always used threaded male copper fittings to connect copper to the shower valve. I generally solder them to short pieces of pipe and then insert them into the valve with some teflon pipe dope. When I solder up the rest of the copper lines, the heat seems far enough away so as not to cause problems with the teflon paste or valve.

Problem is, every once in a while, I get a slight (almost pinhole) leak and end up having to redo the run (since I can't tighten it as it is soldered on the other end). I just demo'd a shower stall and found that the builder used unions (brass I think). This seems like a good idea. What do you think?

Check the valve to see if it will allow you to solder the pipe directly in. Many do. If not, consider using pipe dope, crank it down. The pipe dope isn't affected by nearby heat as much as teflon.