I'm in the school of dig less pull tabs.
The advantage of the more expensive machines (Minelab specifically for this comment), is that the machine gives you 2 numbers; one for conductivity other machine's VDI), and one for the ferrous content. I use an Explorer SE at the beach, and as it's a resort/tourist beach, lined with hotels and each hotel has a 'beach bar', there are literally hundreds (if not thousands) of pulltabs on the stretches I hunt. If I dug every tabs, I'd never get anywhere. I've learned with the utmost of certainty, that on my machine, a pulltab hits at 07-07, 06-07, 07-08, or 08-08. So if I'm getting any of those combinations solidly, I walk on by. I will dig one occasionally as a 'lets make sure this still holds true', and it's always been what I expected it was.
A nickel will ring up as 10-06 or 11-06, down to about 8". I've noticed that at deeper then 8", the ferrous number can be off from that, but I know that a 10-06 or 11-06 will be a nickel. Haven't had those numbers be anything else yet.
Now, there is a very specific reason I will not (for the most part) dig what rings up in the pulltab zone as mentioned above. It's because I can't find any reports or charts of any type of gold having been recovered that has any of those 4 combinations of numbers. If I got a signal that was 09-07, 15-07, 04-08, etc., (in other words same VDI as a pulltab, but different ferrous), I will dig it. I do rely more on the Co (VDI) number then the Fe number, but I use both to make my assessment. Believe it or not, I look for a reason to dig, and not for a reason to not dig.
I still dig every beer can (same Co/VDI as silver and quarters), even when I'm sure they are cans. I dig them because I know that other things of value can ring up the same.
When you are working with a machine that only gives you a VDI, I would say it would be foolish not to dig a pulltab-like signal, as the potential to find or miss something good is greater. But when you have a machine that gives you twice as much information about a target, you're that much more ahead in knowing what lurks below.
I would suggest learning what a pulltab rings up at on the CTX in the ground at different depths. Ie., dig them all, and make a mental note of what each rang up as, and you'll find that most will ring up at the same small range Fe/Co numbers each and every time. Then you'll be able to discriminate them out on a case-by-case basis. There are a couple of pulltabs that don't ring up the same as the majority, and I still dig those. And don't use an air test to determine the numbers; use real digs to see how they report while still in the ground.
Foil is another one I'll happily dig. Small, thin rings have the same VDI as foil, and foil tends to be easy to dig; most isn't too deep has been my experience. Although I am mentally deciding whether or not to eliminate digging foil that has a VDI of 01, as that VDI has never been anything but foil for me up to this point. I will forever dig 02's and 03's, as that was where my second gold rang up, so no chance I won't dig those numbers.
Now don't get me started on ring pulls....