1) they cost less then dosing two-part in the long haul.
2) Get a very good regulator like a Dual Stage GLA / with their lifetime warranty.
3) Pretty much stays inline line and have been using Apex Fusion then added Alkatronic for two fail-safes. With the Alkatronic, test alk about once a week and two weeks for calcium.
4) No but did a ton of research in 2017 and going on three years with no regrets on this current setup.
5) 2 stage GEO, all the way.
Pro - They don't rise your salinity like two-part or full balling does.
Con - If you have issues to maintain a good ph, then a cal reactor would not be the way to go.
You would need to dose Kalk while running your cal reactor if you already have issues with ph.
Tip:
If you run Apex Fusion use the below method (video) and you will not have to worry about clogging while dripping. It was the final straw that led me back to a calcium reactor.
Please take the time to fully absorb the below video.
Do not tie the feed line to your manifold, the water pressure will sway up and down, including doing water changes.
Have rolled with the Sicce .5 pump (as the feed) for three years for the constant stream method and the effluent rate still stays dialed in.
2 stage GEO with a GLA hand made SS dual-stage regulator