Gang, I’ve never been a welder so I don’t know a whole lot about them.
Been seeing these ads now for hand held welders that look similar to a cordless impact.
Do these things really work? Any body know anything about them?
Pros and cons?
Didn’t know if something like this would work for modifying traps( baseplates, laminations, etc)

You can weld with jumper cable and a battery. I read those you are talking about work better than I thought they would but for trap mods I woulf prefer a wire feed and shielding gas or dull shield. Welding is a great ability to have and there are several small 110 welders that would handle what you are asking about and be better long term in my opinion. That said I have never seen or used one like your asking about. Just looks uncomfortable and hard to get into some places

I've seen the ads and such for them

I don't know anyone that personally has one and haven't read any reviews on them.

I have a Miller 250nt on a trailer And the neighbor has a nice wire feed, that covers my needs

there were some decent review videos on them

here is one to get you started

I think the biggest thing is , if you are already a welder and know how to do it you can make it work on some things but if you want the easy option it isn't really it.

Having started my workdays as a welder I may be opinionated. I started welding in the 1960's. Brought the paycheck home with the trade. I have had no exposure to the impact/drill looking units. I do know it would be inconvenient trying to balance that thing very long.
Out of curiosity, I ordered one of the tiny 110V stick units last summer. For being the size of a small shoe box, it does a fair job.
Have used it in remote locations for light duty work.
Keep in mind the machine will not make one a welder. It takes practice and being observant to what is going on.
Do not know what is there but check out u-tube and even better see if the local junior college or trade school offers continuing education classes.