Im only 35 but my o my i use to make fun of my dad for wanting lighter tools. I will carry a m18 tools if i need to but im finding myself use m12 stuff if its the same tool. I have a john deere 550c think cat d5 and a bobcat along with some trailers that i need to grease. I figure the m12 would suit me as im not doing it every day, but i do it enough where it would be nice to get grease flowing through the tough zerks on the dozer. Skookum as frig must be a so-cal thing we dont use it up North.
Just a friendly reminder, this is the deal thread. Of course talk about deals, but there are tool thread that often already cover this.
But for the grease gun, it is really a hard call. 90% will be fine with m12, as it is in between the M18 settings as far as pressure is concerned. So like most that don't grade regularly enough, the m12 will definitely make things more enjoyable and not make greasing a 2 man job (without locking fittings etc).
Now, if you are doing larger equipment or maybe older farm implements, you want the m18. Need the low speed for higher pressure on plugged fittings, and high speed for those large fills. And on large equipment, it often gives you the pump amount in the manual, which you can set on the m18.
If this is for homeowner, you will be fine with m12. If you are Tim Taylor home owner or have have large equipment, grab the m18