I’ve been running the cheap BRS branded ones. So far they have been working fine for me.
they are a few dollars cheaper, and seem to work just as good as the others. I use there brand for the resin and the filter too. I have not found any reason to switch.
Good luck
I use three different ones. I know BRS says that their blocks are just as good if not better than the others but I use rodi water for my business.
I do a matrix chloramine block, BRS block, and a spectrapure chloramine block in the third chamber. I also run a chloramine monster block before all these.
I was using two BRS universal blocks, but just switched to Spectrapure 1 micron > 0.5 micron. In theory, if using multiple blocks, you should use a smaller micron in the second canister to catch anything the 1st block missed.