My interest is for a Mustang, which is rear loading only (I think). The JMJ comes with Fender flats as standard so, apparently, no problem there. However, I use cobalts on my Maruszczyks and like them very much, therefore, I might want to try them on a Mustang (when I finally acquire one). I also own a Rob Allen that comes with LaBella flat, nylons. These are definitely rear load only and I haven’t had any issues with the acoustic type bridge causing splitting or unraveling. A ‘normal’, electric bridge might be another question altogether.
With regard to the difference in tone or tension, I had a Roscoe Beck signature that allowed for either top or rear loading. I tried both and couldn’t feel or hear a discernible difference. I eventually had it loaded E&A rear, D&G top - I don’t know why.