Hi Matt - Would I rather have all self-contained battery locos - Yes. And I now have two. Can I afford to put on-board battery, r/c and sound in all my locos? No. That’s why I chose trail cars. I have one each for my 1:29 and 1:20.3 stock. Both have programmable Phoenix sound cards and a large speaker plus will power speakers in connected locos.
My layout doesn’t have any switching puzzles, I have several industries that I switch, but all can be managed with the trail car attached.
Trail cars are the quickest way to get started in battery r/c if you have a large roster of locos. If those locos are per-wired Aristo locos it’s even easier.