I've just started dipping my toe into the water with the Marriott LNF and so far things are going quite well
I've consistently received repsonses within 24h and hit a 2 for 2 success rate last week!
3 nights at RC Budapest from 340 EUR to 177 EUR per night
1 night at the Prince Sakura hotel from 47,530 JPY to 20,400 JPY
On the second one I did have to email back and forth several times for the correct rate adjustment, my comparable rate showed the all in price including tax but the LNF team were taking this, deducting 25% and then adding 18% tax back on top.
I got there in the end though!