I think it depends on what you have in your reef tank. If you have a wall-to-wall SPS tank IMO trident (or other alk testers) worth every penny. On multiple occasions, I forgot to restart my calcium reactor pump, and although the ph in the reactor itself did not change, my alk and CA dropped substantially and very fast. One time I ended up killing enough SPS to buy a trident and at least 4 years of reagent supplies. Immediately thereafter I purchased a trident to avoid this issue in the future and it helped me on several occasions already.
An additional benefit of the trident/alktronic is it allows you to monitor the overall health of your tank by showing you the alk consumption chart. A few weeks ago I dosed fluconazole to get rid of byropsis, and my alk went from 7.1 to 9.8, this allowed me to stop dosing alk for a while and probably prevented a few burnt tips. Another observation I've had is that when my alk and CA consumption starts to decline steadily, I immediately test my PO4 and No3 and one or the other usually comes out to be close to 0. So trident essentially gives me a warning sign if my nutrients bottom out.