mythic charms and rarity charms do stack with each other. using a mythic charm on its own gives you a 2.5% chance of forging mythic gear, while using one alongside a rarity charm increases that chance to 5%. you'll definitely want to use both a rank and rarity charm anytime you use a mythic charm.

i'll be keeping a tight hold on my mythic charms for a bit while i build up some reserves but once i do start using them, i expect i'll be putting the bulk of them into lethal.

mythic charms and rarity charms do stack with each other. using a mythic charm on its own gives you a 2.5% chance of forging mythic gear, while using one alongside a rarity charm increases that chance to 5%. you'll definitely want to use both a rank and rarity charm anytime you use a mythic charm.

i'll be keeping a tight hold on my mythic charms for a bit while i build up some reserves but once i do start using them, i expect i'll be putting the bulk of them into lethal.

Primarily into Lethal for me, then any Forge Pass sets I manage to earn then Perception.  Thankfully we seem to get a lot of Mythic charms so I don't feel bad using them.  I will only be using them in conjunction with Rank and Rarity too though. 

and substat charms and type charms.  Use all :)

Absolutely.  If I'm going to get crushing disappointment I want it to be worth it.

Crushing disappointment is burning all my reworks trying to make usable maerciless gear today :)

mythic charms and rarity charms do stack with each other. using a mythic charm on its own gives you a 2.5% chance of forging mythic gear, while using one alongside a rarity charm increases that chance to 5%. you'll definitely want to use both a rank and rarity charm anytime you use a mythic charm.

i'll be keeping a tight hold on my mythic charms for a bit while i build up some reserves but once i do start using them, i expect i'll be putting the bulk of them into lethal.

I used all 3 tokens, forged 150+ items and got 1 mythic, so yes small sample size but doesnt look 5% to me at all, more like 1%