For sizing and choosing which flowmeter will best suit, I feel it is very important to do some testing first. I don't find pressure will have much to do with the choice as what goes in the meter, comes out of the meter, and what hits the tank are going to be the same amount unless you have a leak.
But that is about as far as I go on things being the same from tank to tank. We all know counting bubbles is not the same and I find the same with flowmeters as different tanks require totally different CO2 amounts. But there is one sure way to get very close to what amount you do need the meter to measure.
We can certainly go with the idea that the meter which reads a broad range will fit more tanks but that comes at the price of loss of precision in the metering. If your car speedometer reads 0-140 with marks every ten MPH, we do not get the same precision as we get with a meter that reads each MPH! Same with any meter, so getting the one which best reads the range you want, will automatically give you better precision.
So if you have the tank set and working, so some testing first. Stick the end of a CO2 tube up into an overturned vial, etc. and measure how much CO2 you are adding and then go to one of the online conversion calcs to figure how much that is in the type of flowmeter you are looking at buying. You may measure in CC per minute and want to use a meter speaking cubic inches per hour, so some calculations/conversions may be needed?
For my use, I do not find the valves on any of the flowmeters to be precise enough for what I want and I do use needle valves, even when the meter has one on it.