I have been using both APX 100 and APX 400 for a while and I like them both. I did some testing and found that with my developing methods it was better to rate the APX 400 at 200. I've used HC110 and the Ilford version of this (Ilfotec) with good results. I develop at the recommended time as if shot at 400.
I recently picked up a couple of older Yashica TLR's (6x6) and have been using just APX 400 in them and I have been very happy with the results.
I use it to shoot some landscape and old buildings.