Thanks for the change-of-name info on the preset - the --preset portable setting seems to have been renamed to -V5 in newer builds of the alpha. Other than that, it doesn't seem to generate files that are different at all. -V5 gave me identical files on a series of encodes to those generated previously by --preset portable. Ah well, at least I know where it has gone
As far as quality goes, -V5/portable is good enough if you are using ear buds on a portable, where external noise hides any of the slight distortions in the sound. However, I never use it for encodes that get played through a hi-fi/speakers or my good quality headphones - although it still sounds reasonable, the artifacts are more obvious, and there's no point if you are storing files on your hard disk cause you don't need the bitrate saving. I generally get files that range from ~100kbps up to ~150kbps depending on the music obviously. I would say that the only way to see if the quality is good enough for your purposes is to do some test encodes and see if you can hear/live with the artifacts (which are impressively small considering the bitrate) - and remember that the next alpha release might change sound-wise and bitrate-wise for this preset (both upwards and downwards in some cases!) so beware when messing about with alphas
PS. I tried preset 130, but it didn't give me personally as good sound quality vs. bitrate results, so I stuck with the VBR portable preset for my portable. But as with all audio encoding, I'm sure that this is at least partly down to my particular collection of music! So I guess everyone should try both and pick their fave

PPS. Sorry about mis-crediting Rarewares to John - I just assumed it was John's because he always seems to be the one posting about updates to it.