The GI issues are caused by the creatine absorbing water. This causes your gut to have more water than usual as it follows the creatine through the works… which causes… urgency.
The effect diminishes after you’ve been taking a regular dose for a while, even with just monogydrate (not HCL).
Some people say HCL causes less distress because it doesn’t draw water as much. Others argue that defeats the purpose of taking it.
Monohydrate is studied to death and proven effective, HCL not so much.
But otherwise, I'd agree that monohydrate has significantly more research behind it and I'd default to that if it's tolerable.