I use two (sometimes 3) auto dispensers going at the same time. One is throwing while I'm loading from another one. With two or three going, I always have a charge ready and waiting when I crank through charging and seating on my Turret. It's not as fast as an activated powder measure on a charging die, but it lets me weigh every charge, so I don't mind going a little slower.
The process you're describing combining a conventional powder measure and a "finishing trickler" isn't done with products like the AutoCharge or Chargemaster. It's done with an auto trickler, NOT done with an electronic powder dispensing unit. There are auto tricklers out there, which take feedback from a communicating scale, so the primary charge is thrown, then trickled to complete the weight. Those are very different machines than the AutoCharge or Chargemaster. Using an AC or CM in that way would be a massive waste of time. If you want confirmation of your AC or CM, buy two pans, grind them to the same mass, and use a balance beam like an RCBS 505 to confirm each weight. Manually trickling on top of a Hornady unit wouldn't work - it would cause an error code for the dispensing programming - it's made to throw the total charge, so if you targeted 25.0, then trickled manually up to 25.7, it would beep loudly, give an overcharge warning, then you'd have to waste time dealing with the error code. These tools are accurate to +/-0.1grn, which is considerably more accurate than your charges really need to be, and really just about as accurate and repeatable as any Lee Safety Powder Scale or other cheap balance beam can be.
Do not buy a Hornady LNL AutoCharge, they have a very common programming crash problem, and Hornady knows it. They'll throw fine for a dozen or so rounds, then start over throwing by 0.2grn, BUT BEEPING TO TELL YOU IT'S A GOOD THROW, then when you restart, the slow speed (finishing) trickle won't start, so they just stall part way through the charge. You'll unplug and restart, it'll throw two or three just fine, then stall again. Unplug, restart, throw two or 3, stall... So instead of making about 15-20rnds in 10min, it takes about 30min to build 10 rounds... At that point, throwing with a powder measure and trickling and trimming becomes faster. When you call Hornady, if it's inside your 1yr warranty, you get a new machine, because they don't do repairs on them. If it's outside of 1yr, you're SOL. I had 3 units go bad on me. The first one went bad about 6months out of warranty (18month life), two within - meaning under 1yr. I'm 2yrs into my 4th machine, but I don't use it much, as I've placed two Chargemaster's in front of it in the pecking order. Only when I run 3 machines at the same do I have the Hornady running. I LOVE Hornady products, and I really like the more compact size of the Autocharge, and the feature set is very easy to tune and very fast and accurate - until it isn't, and once it goes off of the rails, it's just done, and there's no real support from Hornady. It's a common problem for their unit - turn on your google machine and you'll find a lot more experiences just like mine.
You'll also find a lot of morons talking bad about the Hornady unit over-charging, simply because they don't know how to tune the trickle speed at the finishing end of the throw. The default programming always over charges because it doesn't slow down early enough, but a quick tuning step does slow it down. You'll find similar reviews by Chargemaster users which claim over charges with bulky powders simply because the dudes don't realize a drinking straw would solve all of their problems. Ignore these posts - but don't disregard the other posts regarding the Hornady programming crashes.
Comparatively, I bought a used (~3-4yrs old) Chargemaster in the late 1990's, used it for about 5yrs before selling it (so 8 or 9yrs of use without any issues). I bought the older of my current two Chargemasters I believe 3 or 4yrs ago (trying to remember how old my boy was at the time), then bought my newer one 2yrs ago. Nary an issue.
I leave my Chargemaster's on all of the time. As with any electronic balance (I've been managing lab equipment for over a decade), leaving them on all of the time doesn't hurt anything, and is the best way to combat drift and ensure repeatable charges thrown.
