Temp HPs are awful for a Second Wind mechanic, because the best time to get temporary HPs is before you take any damage at all.
You'd have to rename it to "First Wind."![]()
The fighter in my group has it, and it's pretty bad since it costs an action to use.
Now with them adding more stuff that uses this "bonus action" aka minor action, the game has moved one step closer to 4th edition. It's getting dangerously close now, because it the PHB level 1 fighter can get lay on hands without even reaching 3rd level as an eldritch knight, or taking a feat to have access to Cure Wounds, then we have an insane incentive for mages to multiclass into fighter for two levels.
I've built a battlemage, all you need are two levels of fighter, then five levels of mage, then three more of fighter (in whichever order), and you have a supremely tough character who can pretty much win any one on one battle vs an enemy spellcaster due to con and str saves as well as much higher HP, a nova capability which is the only way in the game to cast two spells in one round (three if you include swift), or a spell and a normal series of attacks as a followup.
Blasting two sculped and empowered fireballs in a row is pretty much guaranteed to wipe the floor with any number of monsters, and those that are left are going to have a very hard time finishing off the PC with the highest defenses of the group. Getting a concentration / constitution saving throw onto your saves list is the icing on the cake for mages to multi into fighter.