I checked out the World Preview Mod and it seems pretty cool! I love how it adds new biomes and structures to explore, as well as new items and creatures to encounter. It adds some fresh content to the game. I haven't had a chance to try it out with the https://modbay.net/mods/157-unofficial-mowzies-mobs.html yet, but I can imagine it would be even more exciting with those additional creatures. As for whether or not it should be allowed, I don't see why not. It's not like it's cheating or anything, it's just adding more variety to the game. Of course, it's always good to make sure mods are compatible and won't cause any crashes or other issues.