I found that my new Garmin Edge 520 will not attach onto the out-front mount while it is in the silicone case. This is because the bracket snags on the case, gripping and distorting the case. To fix the problem all you need is a small spacer under the quarter turn mount. This is barely noticeable but means the Garmin attaches with the silicone case perfectly. One note of caution: with the offset in place the screws securing the quarter turn mount to the out-front bracket obviously aren't quite as far into the mount. It seems secure enough with the original screws but it may be advisable to replace with 1mm longer hex bolts.