I have a bad knee and can’t hunt like I used to, so when I bought my new Swarovski spotting scope and the 115mm lens,I considered getting the BTX eyepiece at that time. Because it is fixed power, I ended up buying the ATX eyepiece… Fast forward a few months and I decided to pick up a BTX and a 65mm lens. I have 7 kids who are all married so we do family events watching eagles, finding bighorn shee, mountain goats or elk. I have enough people to keep my optics busy. The modular system basically makes me have 2 spotting scopes. The only problem I now have is everyone prefers to use the BTX because of how much easier it is for long viewing sessions. My family still love the ATX, but the BTX is now the family favorite. It truly is a game changer!