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Hi Tim,
The difference between an LPR and a UHC is the colour of the light they let through. A UHC will block out most light except for a very small range of colours that come from emmision nebula (like orion), this in effect should make stars, sky etc darker while leaving the nebula just as bright as before - hence increasing contrast. An LPR is similar, but its main purpose is to just block the colour of light that comes comes from sodium street lamps - this doesnt give as good of a contrast improvement.
I own a Lumicon UHC and I can tell you that the improvement is there but dont expect it to work miracles - I would expect that an LPR would do very little. (Caveat - I live in the outer suburbs of melbourne, so perhaps my light pollution is low and thus I dont get as much of an improvement from filters).
When you are paying over $100 for a good filter, I dont think you will mind screwing it in and out a few times! If it really bothers you, sometimes it is possible to screw the filter into a spacer, that can stay in the focuser barrel, then you dont have to do any unscrewing or buy more than one!
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