Ha! Logged into AN for the fist time in months. Coincidentally, I just got a standing desk today.
Just like you,
turtle, I bought only the legs. ApexDesk Flex Pro with the BT compatible memory controller for $313. (I liked the design better, and have no intention to use BT.) Reused the top slab from my old IKEA desk. In fact, I was impatient and lazy, so didn't even remove the old legs. Just slid the assembled mechanicals under my old desk, and promptly lifted it up!
So far, I'm liking it a lot. I suspect I'll have to get some sort of padding for the floor. I can't see my knees and hips taking kindly to standing all day. Do you recommend the mat you got? If so, do you have a link or name?
The other thing I will have to sort out is monitor viewing angle. I currently use an MBP. With a sitting desk, it's easy just to hunch over your keyboard and low laptop screen. However, standing with good posture, bending over isn't going to work. I guess the ideal solution would be an external monitor on a swing arm. But I'm not ready to make that jump just yet.