Should I buy a trail bike or a set of new pick-ups for LP Studio?
No matter how I phrase this reply, you won't like it. The short answer is...KEEP $AVING! A) You will NOT find a good (new) "trail bike" for a mere $400. You're only hope would be to find one hell-of-a-closeout sale or possibly an immaculate used bike 100% certified by a mechanic to be in top-notch shape. 99% of the time a used bike is nothing but someone else's headache. Start thinking a minimum price around $550 and up & up & up... https://www.giant-bicycles.com/us/talon-3 B) If you own a true "Gibson" Les Paul, I wouldn't let anyone touch it expect an authorized Gibson repair dealer. True...many companies make a Les Paul lookalike - including Epiphone, a division of Gibson. But NOTHING beats a true Gibson Les Paul. Why take a chance of screwing it up? 🤔
A $400 mountain bike will probably not be able to stand up to very intensive use, especially if you make the mistake of trying to obtain dual suspension. Put the money away, save another $400, and then buy a decent hardtail mountain bike. It will save you tons of repair money down the "road". Of course, you won't be riding it much on the road. Don't buy something because you have some extra cash. I never buy anything impulsively, over the last 65+ years I have learned too many times that impulsive purchases seldom pan out.
Did I see you write "investment" and "mountain bike" in the same paragraph? With "investment", people generall mean things that hold on to, or increase their value over time. It is VERY rare for ANY kind of bicycle to be considered an "investment". For a MTB, it d be doubly rare. Even if you never crash, it ll depreciate so fast that you ll almost hear the sizzle of money evaporating.
There are no decent quality new bikes of any sort for that kind of money. Add another $1000 or so and you're moving into reasonable quality territory for a new bike. A used bike maybe, but you need to know what to look for to make sure it's in good condition. A bike may very well be an excellent investment in your health, but it's vanishingly unlikely to be a financial investment of any sort.