It's free for me. All atm fees are reimbursed.
As far as the conversion rate goes, I opt out of that on the ATM during withdrawl, but obviously get back baht not USD, so I'm not sure what conversion rate is used, but it must be my banks rate in the USA I'm assuming.
Anyhow, it's much better then the Thai banks rate, I know that for sure as a couple times I accidently pressed the wrong button for conversion and was hit with a pretty high deduction.
Anyhow, I only withdraw for living expenses and pay cash everywhere so it's not worth the hassle of juggling wise, a thai bank, etc. for a slightly better conversion rate somewhere and figuring out what that is. I'm not a plastic guy. I prefer cash.