I had a recent bad experience with Reefkeeper. Before you consider one, I'd highly recommend you attempt to contact their customer support. When my RKL lost it's mind, I was completely unable to contact the manufacturer for support.
I'm unsure where the OP has heard about hard to keep calibrated controllers... IMHO, this is not the case.
For cheap, Inkbird is the way to go. Set your heater's temp control, if it has one, to a degree or so warmer than you want your tank, and plug it into the Inkbird, setting it at the temp you want. It's a fairly safe configuration. You have to have two devices fail for the heater to cook your tank.
With a controller, I'm using an Apex, you have more flexibility. Starting with an email alert if the temp ranges outside of your intended range. It's also fairly easy to add a 2nd temp probe to an Apex, and keep a running comparison between the two. Even possible to set up an alarm if the two probes disagree by more than X degrees. Kill your display lights if the tank temp exceeds a given temp, turn on a fan automatically, etc. Lots of options, with a full controller. I've never needed to calibrate my temp probe on my Apex, but I haven't had it very long, either.
I _love_ the pH monitoring. Aside from nifty graphs showing how much the pH bounces every day, you can set it up to turn off your ATO if you're dosing Kalk, and your pH goes above a certain level, same with a calcium reactor on the low end.
Salinity is a bit less important for me to monitor... I check it when I do my biweekly water changes, and have a well designed ATO system that I can depend on. My salinity just doesn't vary, so I don't see much of a benefit in monitoring it.