Does Usb-c to thunderbolt 2 adapter work with Imac (27" mid 2010)?

That is correct. The adapter does work, but unless you will be connecting, say, a display, but not external drives. For faster disk access externally, use the Firewire port instead of USB.

to a degree, I'd say it will depend on what you're trying to connect...

According to my information on that model there is no Thunderbolt port. It does have a Mini-DisplayPort that uses the same connector as TB2.