Provided that you're using armor with any kind of offensive bonus on it, go for it. Jelly/Skelly/Grey Owlite are now worse than their 4* versions until level 8.

Similarly, don't waste fire crystals heating your 5* offensive armor.

For two pips? What's worth more: two pips or last stand?

Two pips can account for a lot.

@krakob

Once you find a good 4-5 pieces of armor (4-5 being based on chaos set+mercurial demo set+black kat hat, the items I personally use most), you'd want to stick with that setup almost indefinitely. If it takes 300 fire crystals to heat a piece of gear, that's 1200-1500 fire crystals. I believe that 5* fire crystals cost 700 CE for 50. That'd mean spending around 16,800 - 21,000 CE.

You'd better REALLY like whatever your spending those fire crystals on, because 16,800 CE is enough to buy 10-13 entirely new, unheated, 4* weapons from the supply depot. (Heating is unaccounted for here due to the nature of how common shinning fire crystals are)

So, Ms. Krakob, are two pips of health worth 10-13 4* weapons?

-Disclaimers-

Now, if you can farm UFSC, it might be a bit more worth it to heat 5* gear. But if you can farm UFSC, you probably don't need to heat whatever it is you're heating. A decent argument, but one with a bit of a flaw if you ask me.

My calculations above simplify things greatly. It takes over 400 crystals using all 100% forges; this accounts for successful+unrealistic gambling.

Yes, armors give you one pip at level 5 and one at level 10. Yes, heating to level 5 isn't so hard. But even so- it takes 72 fire crystals to get there, and you give up heating a weapon. Would you rather have 1 pip of health, or one level of CTR on something like a haze bomb? 72 crystals is also a little under 1/3 of the way to level 8; the point where 5* weapons become worth it.