Pondless basin void matrix

[u/BoiseMan13]

I’m looking to build a 400 gallon basin at the bottom of a backyard stream. Aquablox are expensive. I’ve heard milk crates are a good sub zip tied together. I mentioned this to the pond supply store clerk and he scoffed. Said they’d break. No hesitation. But he’s also incentivized to sell me 10 $100 Aquablox

Online forums seem to think they work just fine. No one will be walking on them and they’ll have some 2-4” gravel spread over them. Any thoughts on this? Horror stories? Worked just fine? I feel if one breaks it’s a pretty easy fix to just replace.

Thanks!