A calcium reactor is a great idea for a tank of your size. The main reasons why people go with dosing manually, via dosing pumps or just dumping it there are the following (well, mainly):
1) Initial/up-front pricing. You can really spend a lot with a proper Calcium Reactor setup. All items included (pH monitoring, gauge, cylinder/CO2, media, etc). For monitoring my pH, when I was running one, I used 2 pH monitors. One to measure what came right out of the calcium reactor (effluent) and one where my drain from the tank was (all items in sump area, of course). This way I had a way of seeing how much of an impact my reactor's effluent was on my entire tank.
2) Un/ill-educated. This kind-of goes without saying, but it takes a long time to truly understand what your tank needs. It took me 3-4 hours and a case of beer to figure out what all this "stuff" did. I know now, and to be honest, I'm flying this route next go (dosing pumps and two part at the ready).
3) Dosing is too easy not to "at least" try. Some "heavy hitters" in our hobby actually have to resort to dosing (with peristaltic pumps) 2 part, Kalk,
AND run a calcium reactor all the time. These guys typically have "clam habitats" and/or SPS gardens though.
I've never gotten that far, but I'd absolutely love to. I will be more than happy to do all of the said items to sustain a reef that makes me smile.
Any way, that being said, I believe that Dennis was just stating the easiest, cheapest, up-front method that would serve you fine for years. In a 40B you'll never need to dose anything more than what 2-part and some dosing pumps can provide. If you want to set-n-forget, or possibly buy for future upgrades, a calcium reactor may be just what the doctor ordered.
So, how deep are your pockets?
That's the true question. Money now, or money slowly over the next few years... It's all preference.