Okay, it has been a week since this post and there have been no answers. Allow me to share my opinion.
I am not a fan of any equipment you have to modify extensively out of the box to make it work nicely. That said, the BM Trailmaster can be modified relatively easy with some Nomex felt and high temp silicone sealant. Making a charcoal basket helps too.
Rust does appear to be an issue with the Brinkmanns, especially if they sit for long periods unused in winter. If you are handy with a metal brush and a can of high temp paint, you can stay ahead of it. You can spend significantly more and avoid the rust issue for the most part. Ten years seem to be about the longest I've heard BMs lasting but there may be folks who have had them longer. I've read of some folks finding their equipment unusable in as little as two years. The Brinkmann folks can best help you here.
Since this is your first smoker, any smoker you buy will have a learning curve, not only for your equipment but for your techniques. Having an analytical nature helps shorten that learning curve. Folks here can help with that, the learning curve, not the analytical nature.
Horizontal smokers require more tending, which can be tedious on long smokes.
Sales pitch begins now: You can do all the above, or you can buy a Weber Smokey Mountain as your first charcoal smoker, not deal with the rust, no mods are necessary (though they can be done as I have), it will last a lifetime, it can go hours and hours without so much as a glance, and the learning curve is relatively short regardless of your nature.
For a first time smoker with no experience, start with something relatively easy to use so the successes come quickly so smoking becomes a lifetime pleasure. As an engineer by education vertical smokers just make more sense to me (heat rises), but horizontal smokers work great too if you understand what is happening in the smoker. It took me decades to get into smoking meat because the friends I knew with smokers all had complaints. Complaints are few with the WSM.
I'll step aside now and let other folks share their viewpoints.
Whatever you get, have fun!