When you say “lower strap pins” do you mean they don’t have an endpins on the bottom of the guitar? Most guitars come with an endpin. Some come with a strap button located somewhere like on the heel of the neck, but many do not. I don’t know that I have seen a relatively modern guitar without an endpin (or a strap button or jack/button combo in it’s place).
As far as adding a strap button, if you want to play with a strap, I think a strap button the best way to go. I do have a classical guitar, and it lacks a button, but a heel strap button is abnormal for a classical. I am kind of picky about where a heel button goes. I have one that was just kind of slapped on there by a previous owner, and it bugs me a bit. I still bought the guitar, but nonetheless. Probably just because I am a Martin guy, I like the Martin spec for placement. Here’s a quote from the following thread "50-50 seems to be the mathematical descriptor, i.e. halfway along a line from the fingerboard to the heel-cap, and halfway along an imaginary line from the front of the heel at the body to the back edge of the heel."
theunofficialmartinguitarforum.y … Y6xQaJJNWI
Some will argue that it devalues the guitar, but in my experience, that has not been the case unless it is done very oddly or very poorly.
One last thing, with some smaller instruments, a heel strap button may not do what you want. I bought an A style mandolin and planned on putting a strap button in the neck block. However, I played with it slung simulating a strap button and the balance was very head heavy. I ended up just slinging the headstock, and I love it like that.