My lee kit includes 2 holders and tandem adapter (professional kit)
0.45 ND Hard Grad (1.5 stop)
Square circular polariser
10 Stop Filter, could not get a big stopper at the time.
Lee 10 filter case, hard backed with velvet pockets.
also lee lens caps, adapter rings stay on my lenses
Wide angle hood (2 slots).
I got the square filter because it is a lot cheaper, can be put in normal or rotated 90 degrees giving full or half polarization. for finer control planned on using the secondary holder.
I wish I had not got the two holders but just got the hood earlier. The hood can attach to the tandem adapter, using up one slot. Or the more expensive round circular polariser can fit inside the the lens hood and rotated separately.
I believe the issue is due to resin filters but sure some one will shoot with the real reason, the filters can handle flare really badly in some situations so having a hood or shading the glass from out of shot light sources is a really good idea.