I've used the Cat stove and ended up staying with the Penny stove - the penny was one of the easiest I found to make simmer, but I still haven't found an alcohol stove that isn't too "fiddly" for me trying to make it simmer in field conditions, The cat stove was "much" more finicky trying to play with strips and all sorts of contraptions.

My solution has simply been not to bother with simmering. I have a good cozy for my pot, and I take anything that can be made with boiling water and a cozy when backpacking on an alcohol stove.

If I really want to simmer or do fancier cooking, I take a canister (snow peak) stove