Non steroidal AI's (Letro Adex) are suppressive and should not be used either for NHA or post cycle therapy. They are for "on" cycle estrogen control only.
ATD is not only used because of price and availability. It is not suppressive and it is effective, that is why it is used. 6-OXO can be substituted but is much less effective IMO.
The reason for the side effects reported with Letro is due to it's effeciancy at totally destroying estrogen. Even a low dose can effectively eliminate to like 98%. ATD has a high side effect profile as well, you should lower the dose accordingly to offset any sides.
Powerfull, DHEA and fenugreek are great additions to the NHA stack btw.