Hi,
I've got some manipulation cards, but they are not Nielsen manipulation cards, so i can't comment on the quality of these cards. The cards i have are Peter Marvey cards.
When i first started with manipulations i got the "art of card manipulation" video's by Jeff McBride. On one of the tapes (i thought it was volume 2) he shows how to prepare cards for manipulation, so i used normal poker sized bike cards.
When i got the manipulation cards they were bridge sized. I prefer the poker size because they are just a bit bigger and give some more room to grip the cards, which i find very usefull for back palm productions.
The manipulation cards are very thin, so let's say your limit for back palming normal cards is 10 then you can back palm about 20 to 25 manipulation cards, so you can produce a lot more before you have to 'steal' some new cards to produce.
The downside for these thinner cards is they are easy to fold and wrinkle if you happen to produce the cards a bit sloppy. Also the 'snap production' seems to ruin these thin cards (or maybe i hold them to tight ?)
Also i don't like the way these cards fan, cut or shuffle. Again, i cant comment about the Nielsen cards, but the Marvey cards are only for manipulation, no fancy show-off moves.
As for fanning powder, it's a powder that should make old cards smooth again so they become easy to fan. See the link below for another thread about fanning powder.
http://www.talkmagic.co.uk/ftopic6784.p ... ght=powder
So, my conclusion for manipulation cards:
I don't use them, i use normal bike cards that i break in a little by bending them. Practice with these cards for a while and they will get looser for manipulations. I don't use powder on them. The bike cards last a long time, and when they get to sticky to use, i just throw them away.
Hope this helps a bit.