coolant overflow...sometimes

Short version:
-random overheating every 5 months=take it to a shop
-magic water test by 2 mechanics that say blown head gasket (no other assessment)=quote of $2000-3000 repair
-used Blue Devil Head Gasket sealer
-took the third mechanic=compression test on all 6 cylinders look good 180-190
-sometimes coolant overflow reservoir is way above full or spilling out, next day it's right at the full line
-So, WTF does this mean and what do I do?

 

It means blown head gasket. Just like two professional mechanics said
2005 year model is known for it. Out of curiosity, how many miles?

https://www.tacomaworld.com/threads/05-06-tacoma-head-gasket-failure-poll.595994/

 

150K miles. SO even with good compression, it's blown but perhaps not badly?
What's the harm in keeping eyes on the coolant and just keep driving it?