IMO simple common sense surrounding the handling of the cylinders makes them relatively safe to work with. I don't want to discount for a second Geo's perspective, because they are, for lack of a better term... bombs. Being careless with them can be deadly. On the flip side however, very simple safety procedures make them very safe.
Handling one safely is a simple matter and doing so makes them very safe to work with. IMO, it breaks down to...
- Carry them carefully and safely.
- Secure them from tipping over.
- Protect the valve stem
- Do not use any DIY plumbing between the cylinder valve and regulator
- Do not leave them or transport them in a hot car (this includes the trunk)
- Make sure the cylinder is up to date on it's hydrotest
- Do not open the valve without a regulator properly attached.
IMO the biggest single drawback of calcium reactors is their up front expense. Once you get that out of the way, it's nothing but positives provided you use them correctly. They are dirt cheap to operate, do a better, cheaper job than ANYTHING else to maintain calcium and alkalinity, and are pretty hands off once you get them set up apart from basic maintenance.
I have a Korallin reactor myself which works very well, but it was expensive and getting inside the chamber can be a real pain.
If there is any drawback other than the cost, it would be that if you don't set it up right or if your system has extraordinarily high calcium demands (necessitating a high Co2 flow rate), it can cause a pH drop in the system, but this can be countered easily by dripping kalk along with your reactor.
