Depends a lot on what you're hoping to use it for. As a help for a poor quality water source they can be fine. In line in the tank, only ever seen things like that on the more complex sets.
I've made up a python system to refil my tank when doing water changes, but I'm still not confident when adding dechorinator to my tank, so I was thinking of fitting a hma filter or a dechorinator filter I'm not sure so seeking more advice
Ahhh, now for those, they're fine. Some of the bigger tanks use them on constant trickle mode, otherwise it's worth noting that they're not the quickest of things, so you may want to look at the rate of water output from them.