I've been wondering the same. Mine are going on six years old at this point with close to 300 rounds on them, not counting driving range and other practice. So I'm very interested to see what others say.

I should at least limit myself to every other release, but the T series keeps pulling me in with each release. I’m thinking Gen 3 will stay for awhile. Famous last words…
That said, serious golfers might do well to at least recheck their set at least every 3 rd release. Between technology improvements and the damage on our bodies, a comparison of old to new through a structured fitting is a reasonable investment. It’s a $100 to get a fitting if you walk instead of purchase. Playing more than 50 rounds a year, buying shoes and balls, that is a cheap insurance policy to make sure your equipment is the right combo for you.
Playing 10-20 rounds a year, clubs aren’t the biggest hindrance to improving.

For me, it depends on why I am switching.

I had a set of 690 CBs for 15 years, and moved into a new set of miz MP245 for performance and forgiveness. However, I only played these 1 year before moving into a set of T150/250s...

The reason I moved away from miz was an overcorrection in shaft weight. I was going to replace the shafts, but I loved the how high I hit the T series irons during an impromputu fitting and couldn't help but pull the trigger. I can see these being in the bag for a long time.