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Get the floor finish.
This is the traditional way to get a very level and smooth floor with a stiff mix of concrete screed.
And here is one of the many chemical solutions that self level.
But one criticism of some chemical products is they leave a waxy surface that you cannot stick floor tiles to.
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The traditional concrete needs to be quite thick if it is not to crack and have a durable and resilient surface.
The chemical screeds can usually be a lot thinner.
In a basement, thinner means digging less deep and sending less soil away. If you reduce floor insulation thickness and/or screed thickness, you will save money. Plus, you are more likely to remain within the 3m excavation depth limit of your site insurance.
A screed is necessary if you have underfloor heating because you must not put underfloor heating in your structural floor slab. Raising the temperature expands the steel reinforcement bars and they won't be in tension as they are supposed to be. Heating the bars could cause your floor slab to crack.
On the next page I cast doubt whether you really need insulation under basement floor screed.
But the main point is, you cannot get these qualities of finish with waterproof concrete.
Waterproof concrete is stiff and sets fast.
There is already such a lot to do trying to get hundreds of tonnes of concrete fairly level and properly compacted.
Time after time, a client thought he could go back and improve the surface slightly. But it was already too late and they made it worse.
The motorised vibrating tamp rail will give you the best finish possible with waterproof concrete but that is unlikely to be good enough for everyone.
It could be good enough to tile on a thick bed, though.
But what if it isn't, because it was too hot on the day and there was no time?
The best plan is probably to plan to have floor screed, and to dig deep enough to allow it without reducing your headroom.
The time of year is worthy of note. You are likely to have a bit more time to level and finish your waterproof concrete on cooler days without a lot of wind or sunshine.
I like to experiment and I have tried making my own self levelling thin screeds.
I have added a lot of SBR and plasticiser powder to various mixes with cement and Multifinish plaster.
None levelled sufficiently well.
The multifinish did not mix in and I was left with hundreds of bubbles that were actually full of dry powder.
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