I had never heard of slip on winglets for the ASW-24. I bought factory winglets and I imagine virtually all ASW-24's have winglets so that should be a non-issue. As stated before the ASW-24 is a great glider and is worthy of consideration for a new or experienced pilot. Standard class is nice for new pilots, less to think about just fly. The standards lose out on the high end of the polar as compared to flapped ships but that really will not be a factor most pilots.