Never used the stuff. I read somewhere it wasn't all it was cracked up to be. Flattening in a dry-mount press should pose no problems. Follow that with a couple days under some heavy books.
I have made direct comparisons with and without it on several different papers and have only found a slight improvement when using a film dryer (roughly equal to putting it through the dryer a second time). Not worth the effort.
I 've read somewhere that if used first, toning will be blotchy or badly stained, if it works at all. Have also been told by 2 teachers (in 2 different colleges) that it's not really worth the time or money. You'll only end up putting it into a press anyway.
I don't think we will ever get all our prints flat but only come close.
I have used Edwal Super Flat over the years without encountering any problems. Follow the directions and adjust accordingly. You may want to run some test to determine which dilution gives the best results. I prefer to use blotter paper, purchased from Light Impressions. I place my prints on every second blotter paper in stacks of six. I let my prints barely dry damp and remove to screens to complete drying. To reach barely dry damp prints may take 4-8 hours pending on how warm the room is.
If TLC for those fine prints is your concern you should consider
the blotter stack method. I use ventilation class corrugated board
in conjunction with hydrophobic separator sheets. The "hydrophobic"
is an innovation on my part; improving on an age old method.
I've a source for the board if you're interested. The hydrophobic
can be picked up at any fabric shop. Dan