If you haven’t already, I suggest getting some basics through these two sources
best practices summarised by dr cliff
And they have article about listening in noise, also recommended to read.
Both sources have youtube channel if you like that media instead.
In short - tech level of aid you need depends on your lifestyle and environments you’re in, and your brain’s ability to decipher the information from the sounds it gets. Namely, if your WRS is low, no money will make the difference. If your SNR is high, even highest level won’t do it, maybe mics can help a bit, but it still depends on that number. (you don’t need that number to know your brain is useless in noise, we mostly know that, it’s just more convenient for fitter to see black on white, and also for you to see if your needs go above what any aid can provide, they’re currently on roughly 4-6 db so if you need 10, you can see why aids alone just won’t work with you)
In quiet, low level and flagship perform the same. Assuming they’re both properly fitted (using REM based speech mapping).
However, any background noise makes it harder, for aids and your brain, if your SNR is high. Mind you, high is everything above 4 db. 10 is insanely high 
Level up of difficulty is when bg noise isn’t noise but voices, eg restaurants, where there’s speech babble.
If you need mic, then it might be an option to take lowest tech plus mic, if highest tech alone isn’t working for you anyway. But it depends also what other perks you want from aid.
So, which tech level, tell us your numbers and your usual environment. If you don’t know numbers, then fitter doesn’t follow best practices, so, it’s very questionable on what they’re making their claim about which tech is beneficial to you, and what else they won’t do properly. In short, not worth spending the money there.
For anyone in the USA I’d say, go to costco.
KS9 if you like that color of sound are superb aids, top level, 1500 a pair if I remember correctly.
But I think they have cheaper decent options as well. People here mostly write about KS9 (phonak marvel).
Ah, uk? I think there’s costco there as well?