Yes, STV is the deal breaker for me. Many of us are former military pilots and one of the worst parts of that life was the unknown TDY. STV simply brings that back to us.
When it comes down to it, the same age old axiom applies: It's all about the work rules.
The MEC knew this when they didn't let us vote on the postal LOA. We left money on the table back then, but we didn't allow our work rules to change which would have resulted in up to two more days of work each month.
The argument can be made that the money in the LOA is better than nothing, but you cannot say the same for STV.