The v2.0 was officially released about the third week of April, 2014, and about 4 months later the v2.1 came out.
Your long-term use requirement should be based from these dates.
Opus BT-C3100 V2.0 "Dreamcharger" GROUP BUY Now @ $ 36. New coupon code - tatasal -(to close July 15) NOW CLOSED - introduction date of the v2.0
$37.99 for Opus BT-C3100 V2.1 with OP3100 ( clearance) & $38.99 for Opus2.2 without using the coupon @GearBest - introduction date of the v2.1