I have a 5 x 5 Secret Jardin and the zipper is kind of funky. It has to be zipped up just right or it creates a gap where the 2 zippers meet. Don't know if it is an anomaly just on my tent or if they are all like that. My other 2 tents are inexpensive ones from E-bay or Amazon and have done just fine. I generally look for a tent that will match my specific needs--for instance (like Hackerman mentioned) the number and placement of the doors is important. I also look for vent hole placement to see if it will meet my needs and be convenient to vent.
One of my gripes about tents is the inability to hang things on the walls. The last indoor grow I did, I cut a piece of pegboard to the width of the tent, attached that to two pieces of 1 x 2 and attached the 1 x 2s to the tent's corner posts with zip ties. This gives you a place in your tent to hang things like thermometers, small fans, cords, electrical timers, etc.