I can't comment on WSI, but I am using XM and have used the Honeywell uplink also. The XM is great, it updates every 5 minutes as advertised with the exception of the Satellite maps that sometimes run a couple minutes behind.
I am using it on the FG 4000 with a bluetooth gps receiver and the portable WXWORX receiver wired in to ships power. Went this way because it works just as good as the certified boxes but at a significant cost savings. I believe the XM product is significantly cheaper also.
The only complaint I have is when using the gps receiver with the XM and then switching to Flight Deck, the gps info comes up ok, but when going back to XM you have to close flight deck to get the XM to pick up the gps signal again. I hope to correct this when we get the second efb and gps receiver.
I also know some guys running the WSI and they love it also.
I think both are good products, I just liked the portability of the XM system.