I have looked at both closely... here are the differences:
1) The Play Pen generally sells for less at retail. $235 vs $280.
2) The Play Pen does have additional outriggers for additional attachments to the sides.
3) The Yakima Loadwarrior has the round bars built right in... the Play Pen's are added on (but included). You can installed bike carriers, ski carriers, and others directly to the basket.
4) The Loadwarrior uses slightly larger tubing.
5) Both baskets come with fairing or wind dam included which is good becaues the fairing eliminates almost all of the wind noise created by the factory rack.
6) No problems with hardware issues with the Yakima. Everything is solid. Install and go.
7) Look at where the two halves of the baskets are joined. The Loadwarrior's tubes meet up nicer compared to the Play Pen.
Both baskets are decent. The Yakima just looks a little more sturdier and has fewer parts. REI had a sale couple weeks ago which dropped the price right down to the Play Pen's retail price so I ended up with the Yakima. If it wasn't for that I would've ordered from www.ageebike.com which sells it for $280 with free shipping and in store credit for free accessories. About $60 worth of credit which is enough to get you the light brackets, locking brackets, and with $5 left to go towards something else like the stretch net.
The outriggers on the Play Pen is nice... but Yakima does have add on accessories that are designed to mount to the side, like a high lift jack mount and s shovel mount. Anyone know if the ligh lift would work on the VX? my guess is not because of the cladding...
It's possible to get the Loadwarror for $160 ($120 off retail) if you know someone who works for a Yakima dealer. I do, but it takes too long to get coordinated so I gave up. My guess is $160 is 10% over dealer cost. Pretty outrageous eh? Pretty good profit margin considering retail is $280.
Ebay is a good place to pickup Yakima stuff new or used. Not long ago I missed out on a Loadwarrior with 3 Steelhead bike mounts ($100 each retail) for $298 total. The problem with eBay is a lot of times you get a lot of idiots who don't understand the game placing their bids too early and get in a bid war with each other which drives up the final price for everyone else.