the RD series is higher end stuff and FP series more like entry level. feature-wise, RD series keyboards have more, e.g editable patches, efx, split/layer keyboard, more sounds etc.. while FP keyboards don't really do much.
i think the RD-100 is quite old already. not sure about the sounds and the key action. but that one bundled with the JV1010 module seems quite a reasonable purchase.
FP is a digital piano. It is meant to replace a piano at home. Therefore it has build-in speakers and no other fancy things one will need to perform on live on stage.
RD is a stage piano - meant for performing in studio/stage etc. Therefore it has no build-in speakers. More sounds, more user friendly for a performer (faders instead of knobs in the FP etc).
The RD100 is not too bad. It is an old model (the new one that replaced it is the RD150). The action is OK but I felt the RD700 to be slightly more responsive than the RD100. Sounds OK - typical Roland sounds. The Orchestral Strings patch is pretty lush. Layering is easy and sounds great. The Jazz Scat sounds are cute but pretty useless. I bought this model for my church about 3 years ago and it is still being used and working great. My favourite layers - piano with orchestral strings, piano with e-piano (with volume of e-piano 1/3 more than piano). However, note that it has no B3 type of sounds, unfortunately. Difficult to play B3 on a weighted keyboard anyway.
What to look for in a digital/stage piano? Already discussed in other threads. You'll need to do a search. But to put it simply, 2 main things - touch and sound. Most important, if you like it, it is for you. Everybody differs in opinions on sounds - can never get a consensus.
YAY!! i've bought a Roland RD-170. =P you're all right... it doesn't have built-in speakers. good thing it can allow two sets of headphones to be plugged in, which i used a pair of speakers to produce the sound.
i know its doing the keyboard a disservice, but until i save up enough to buy an acoustic amp, i guess its either the speakers or a pair of headphones.
for a noob like myself, i think the feel is pretty good. weighted keys to exercise the strength of my pinky.
it has this dual layering effect also where i can choose two instruments and it'll play both at the same time. and volume control for each of the instruments. i like it. =)
mods and admins, please lock this. i'm done. thanx.