It's not the first. Thank You Isekai has much better art and genderswap. these guys looks like total clones of each other. he can't draw male characters
I was meaning first for me. Though you made a good point, I forgot about thank you isekai!(which actually makes this the second, and reminded me to read new chapters).
Also technically isekai bishoujo ojisan could also count since both have swapped(though only one at a time).
Given the plethora of series out there it also wouldn't surprise me if there were others.
I have no comment on this authors drawing ability yet. Maybe he just doesn't do well drawing 2 characters with glasses. (I need a larger sample size of characters to compare before agreeing)
Regardless, I'm not exactly taking this series seriously. Isekai truck turning into mech suit randomly made it clear what kind of series this will be. I'm here for the fun.