I have the regular HSGI sure grip belt. I only used it once at a open shoot. Did not remember getting hot or uncomfortable. Don't know about the slim one but the regular size belt supports a IFAK, Esee 3 knife, G19 in a kydex holster, a taco double rifle mag pouch with loaded standard mags, 2 pistol mags in pouches, a dump pouch and multi tool in pouch. Check out reviews from SKD and Amazon to form a good opinion. If it's 50-50, wait for labor day sale or SKD sale and get both with a cobra belt. SKD shipping is USPS priority 3 day for $5. Sometimes you can get as much as 17% discount at a SKD sale.
I think about using this setup for the proverbial SHTF scenario but for more common every day use, I rely on a Buffalo leather gun belt with Milt Sparks holster for a P239, single mag pouch , flashlight pouch and .357 mag. cartridge holder (holds 12) if I also have to involve my 1894C lever gun.