I’ve got at least three iMST boards deployed outside, in a proper case that is no issue at all.
If you are suggesting the Mikrotik gateway is better value for money, that might be the case, keep in mind it got to the market well over four years after the iMST hardware was released.
Two IMST boards have gone deaf here. After statics in the air.
I asked IMST, the board is not to be used for outside usage as it has no anti-ESD components.
Or you have added the anti-ESD components or you have been lucky.
Lots more have gone deaf by other people.