Concrete or Vermiculite in Massachusetts

My wife and I are considering installing a in-ground vinyl liner pool in Massachusetts. We have narrowed our contractors down to 2. Overall prices are very similar, but we can't quite decide who to use. We are going to do an l-shaped pool, but would like to increase the shallow end from 42" to 48". One installer pours concrete for the base of the pool and suggests we install larger steel panels. The second installs a vermiculite base and said we do not need to install larger panels, they just dig down a bit deeper.

I've done a fair amount of research, but still cannot decide which is better. I feel like the larger panels and concrete base would be structurally stronger, but I am concerned about the concrete cracking and causing issues down the road. I have also read that the concrete can cause the liner to wear faster since it can act like sandpaper.

The vermiculite seems to be softer, but can "cookie" or flake and needs to be repaired as well. It makes sense to me that it can expand and contract to avoid cracking, but also lets water pass through since it is more porous. Seems like this could cause issues as well.

So I guess I am just looking for some input from others on this issue. This is a really difficult decision.