I'm not sure that it's worth buying med probes. unless I misunderstand they're consumable, so once you use them all up...you have to buy more...with actual money. I wouldn't mind if it was in-game currency and you could spend real money to expand your capacity, but paying to not respawn 500+ meters away? No thanks.
Right, but I can definitely see them mostly being used during instances, as it's a pain to die during an instance and having to get all the way back to it, sometimes with the mobs inside having resetted. Or like the bug that I've experienced earlier where dying and being sent back to the spawn point had caused the quest to be unable to proceed further. And I still haven't beat that quest due to the bug making it all that much harder since I've had to reset it. I'd only be using those probes during instances.