To be fair the waterless coolant has a lower heatcapacity than coolant that has part water in it. So cooling will be slightly less.
The waterless coolant is basically glycol, and normal coolant is a mix of water, glycol and some salts (corrosion inhibitors).
Also the heat flux (that is the amount of heat that is transferred through a certian surface) might be a little less.
Normal coolant is probably less viscous and may have a lower surface tension between fluid and metal, so that gives more contact flow between metal and coolant.
With the all aluminium block in your z4, aluminium radiator etc etc and it being driven on a fairly regular basis (1x/month or so) and given coolant changes every few years there is no need. (the waterless coolant having less heat capacity will actually be worse).
This stuff should be used in vehicles like older campervans or oldtimers, that don't see regular use (campervans sometimes only 1x/year) and mostly have iron blocks and different materials screwed on to it (aluminium waterpumps or radiators etc).
Then waterbased solutions can act as a electrolyte and some parts can corrode excessively due to galvanic mismatch.
Also the galvanic corrosion will shorten normal coolants life.
It may be an option to a z4m with the cast iron block, but that engine produces more heat so the heat capacity of the coolant is relative more important.
As long as you don't have problems with boiling steam coming out of your coolant container cap, there is also no need for a coolant that doesn't boil.
Also getting all of the coolant out of the block is very difficult. they have that flushing fluid, and that takes water away, but getting that out of the block is just as difficult.
I tried getting all the fluid out of the block a few months back because I had the waterpump, thermostat and a lot of other stuff loose, but even removing the frost plugs (in the side of the block), setting the heater at max, using compressed air there is still coolant in the block.
If you think all is gone, and you blow compressed air in a slightly different direction, some coolant will come out again.
And from what I understood evans emphasizes that getting all the old coolant out is pretty important.
So the conversion from waterbased to waterless coolant is a pretty difficult job.
And you can never fill again with some water in emergency when your waterpump or radiator leaks a bit (or a cracked coolant reservoir, a typical bmw flaw).
Then you have to get everything off again and purge the complete system.
By the seaside...