Structo lite for base of whirlpool

OK, big box store tried to sell me quick-set cement mix (the green bag) to use on floor of drop-in deck to stabilize the whirlpool. Just did not sound right so I asked a contractor I know and he recommended structo-lite. Am I ok with the structo-lite? Once down I will cover with the polymer & set the tub in.
Has anybody used this before?

You've got your order of operations slightly upset...it will be almost impossible to get a perfect surface to set your tub on if you let it cure before you set the tub...so, put some piles, strategically placed where they'll support things, throw down the plastic (it doesn't hurt to have some on the floor before throwing the piles down - this helps keep the subflooring from absorbing too much water from the mix - concrete products cure, and incorporate the moisture into their crystalline structure...it doesn't dry), and then mush the tub into it while looking at the level(s) so you have it perfectly level and at the height you want.

Maybe there is some confusion here. I am not going to let the mix cure before I set the tub into it. My plan was to put roof tar paper down, lay down the mix at 2x the height needed, cover with polymer & set the tub into it pushing down (standing in the tub) so the foam feet rests on the sub-floor but squashed all around the mix; and then let it cure.

My question was, is stucto-lite a good product to use in this situation? Has anyone ever used it? were you satisfied with it? Would you recommend or not recommend using it?

I have heard of others using it, but do not know what advantages it would have over common masonry mortar.

We set all of our tubs and shower bases with stuctolite. Never covered mix with polymer. Just straight into mix.

Okay, you may find that the tub doesn't squish if you have too much there. Terry suggests putting multiple piles of it down, rather than trying to be at all neat and level with it. Also, if it doesn't sit perfectly level both end-to-end and side-to-side, do NOT push it down so the feet are on the subfloor...push it down until it is level. One or more of the feet may then be on the subfloor, but if supported well, none need to be.