We ran a VHM head on out KTM65 last year. The advantage is that you can easliy change the the head domes and thus change compression for the type of track your going to be racing at, without having to carry extra heads that have already been milled.
There was a noticable difference between the MX & SX inserts. You can also order a blank insert and have it machined to achieve the compression your looking for.