We have one and like it, but I think its functionality really depends on the type of cycling you do.
We bought it to move our then-3, now 4-year old out of the Topeak Babyseat (since we never did a trailer, many of my criticism may be a non-issue for you). She's still well within the weight limit on that seat, but when my husband was riding up hills, he was doing a lot of "wheelies" and it didn't feel stable.
For riding recreational trails, it's great. For going on long rides, where our daughter may want to relax or take a nap, it's a great alternative to a traditional TAB.
But for riding in the city, which is a lot of the riding we do, it's more trouble than it's worth. It's hard to manage in tight spaces (because of the recumbent aspect, it's longer than having a standard trailer attached to the back). She's also much farther behind us and it doesn't feel as safe. Because of the way it's designed, there's really only one place to securely lock it up, which entails us bringing a chain lock with us all the time. It's much easier to just throw our daughter on the Topeak and now we're looking at buying a cargo bike for when she outgrows the Topeak to keep carrying her on our bikes (along with our 2-year old).
Compared to a traditional TAB, it's definitely more stable and it's more interactive for her than just sitting on the back of our bike (although given a choice, she'd much rather just sit on the back of our bike).
We have a minivan and an SUV and we have to at least partially disassemble the Weehoo to get it into the car (taking off the "arm" piece). It's also hard to store vs. a folding trail-a-bike.
We have the "pro" version and it's still pretty heavy; I definitely feel the weight of it when I'm pulling it, although it is much more smooth than pulling a trailer.