Sorry I am chiming in a little late but I have a Silvertip and it is a great little bike that for some reason has no defenders here. I've had mine for a little over 3 years now and it was my primary ride for the first 2 years I put a fair number of miles on it and I can say that it is not near the end of its lifespan by a long shot. Although that could only be because of the superb care I took with it , well I never left it outside over night at least. The frame is fantasticly rigid for a folder, i had thought mine creaked in the lockjaws but it was in fact its square taper cranks. Its a good solid little bike well worth the cost of admission if you can find one.
On the other side of the coin I can say that the others here have a point, I personally don't care for aluminum frames but all frames can crack if flawed or pushed too far. The bike does have a couple of annoying proprietary parts ie the NVO stem, the 74mm front hub which I could do without, and the lockjaw hinge components but that's it for special parts on the Silvertip. I also personally don't care for the radial spoke lacing on the front and half of the rear wheels, someday I will fix that on mine.
I would say that IF you can find a used bike friday that meets your needs in your price range jump on it, you will most likely not regret it (I'm assuming, never rode one but those who have think they roll on the surface of water like a jesus bike). I would say test ride your choice first but that is probably not possible with the BF.