I used to use a similar QuikLok laptop tray with my Z stand, but I fell in love with the low profile of the Keylab tray. I try to keep the laptop as invisible and out of sight as I can, and trays really stick up. But there might not be any better option. I've eyeballed the APEX stand before, but if I remember correctly, they used to be like $400 back when I was buying my last stand. I really like the Z stand for the legroom it provides for pedals and controllers (I swear I have more stuff at my feet every week). 3 pedals, a trumpet, a Wii Remote (don't ask), and assorted props like hats and an old telephone.
As for the Seaboard, I've never gotten a chance to try one, as I don't think any store in my area (Honolulu) has any. I've been to all music stores and Apple Stores and never seen one. I have heard that the keys take some getting used to. I view it as a different kind of instrument that I would need to practice on to get comfortable with. But it really looks like it suits my type of playing, as I'm a big progrock/jazzrock lead guy, and I'd love the immediate control it would afford. I'd put in the hours to get good at it.