When you want to use models instead of regions you have more objects for the renderer/ tree and especially for c_move to process. Other objects (such as effects/ exploding and falling chunks, enemies, birds, ...) will all need to ignore those models too resulting in more work for you. Then, on collision your player will stop mid-air immediately, depending on what you want to achieve this may look bad. In my sidescroller there are bottomless pits and when the player falls from the platform he should not stop for one frame or more mid-aid but just continue falling to his doom while playing the death animation. You could try and use IGNORE_PUSH and a low push value for your obstacle objects, too.

When using regions you can just move and scale them to any size that you want. Checking for all regions can be somehow circumvented when you just use region_find instead and then compare the result. You can call the regions for example "abyssXYZ" and compare for "abyss", then, if necessary, use the number XYZ to determine a spawning position easily.