Awful prestige mechanic. You don't "keep" your upgrades. A respec with prestige is to be expected, but you pretty much have to put them all back exactly where they were to get back where you were before the reset, and you've gained nothing from it.
Also microtransactions suck.
Save works great for me, though one attempt doesn't really make a thorough study. I would like an auto merchant and the option of maxing item stats instead of waiting until one breaks to equip a better one.
Is it every time or was it just for your first time?