I am writing this as it took me a long time to decide to go for these as they are relatively expensive and cannot be tried out before buying. I am certain they are many others in the same position.
I finally decided to try these after using shure /comply tips for some years and never getting a really secure fit in my left ear.
I went to Boots and the audiologist injecting the setting material into my ears which was totally painless. They then sent these off to ACS who completed the tips within a couple of weeks (Boots also give a 10% discount if you ask)
When i tried them out (initially) they felt slightly hard but come with some gel as this is obviously a common experience. After the second time of insertion they go into pretty easily (more easily than generic tips) and fit superbly, i do not feel either are likely to drop out of my ear. As an aside they are probably more hygenic as they do not require compressing before insertion.
The advantages for me besides super fit are increased isolation (a major issue - I can now use them while my wife watches TV without problem) and wider soundstage/superb deep bass which was present with the shure tips but didn't feel so solid. Overall a more musical and envelloping listening experience and well worth the (relatively high cost).
I am using these with se535.
Finally neither the ACS or Boots websites are that helpful in finding them but typing ACS custom tips works.
Edited by magicalmouse - 9/28/14 at 1:10am