What's the double edge you're talking about? Cost? Limited slots?
I get triple potion hit is more powerful than separate potions, it also costs more. I wouldn't spend 50g extra on them "just in case", like I don't spend 50g on amulet of yendor/translocation scroll. It's also a one-shot thing instead of a permanent strength bump. It can be used on a hard boss or perhaps a few bonus xp but I honestly don't think that's worth the price in hard dungeons.
As for multiplication with other preps, trisword being uncapped might be the bigger problem.
At the very least I'd like to see better examples of said multiplicative combinations.