I purchased their 'Professional System II' greenhouse. It is 30' wide, 48' long, and 13 feet tall.
The materials are strong and of good quality, and the equipment (fans, heaters, etc) are from quality brand names.
There was a problem with the delivery of the greenhouse... the company who they had contracted for the shipping contacted me the morning of the delivery, and told me that he refused to turn into my driveway (I have a steep driveway, but it is manageable).
I called Growit and they took care of it completely, arranging for a different driver to come and deliver the greenhouse. The very next day, he arrived and came all the way up to the house.
Additionally, the motor for the fan didn't arrive with the rest of the gear. A very short call to Growit, and they had one expedited out to me with no questions asked.
The manual is extremely poorly written, so I had to "figure out" a lot of the putting together.
These greenhouses are definitely NOT for the novice handyman. But, if you have built stuff before, and aren't afraid of some medium construction, by all means, this is a great company to get your equipment from. Today, I have a great greenhouse with high quality equipment, and am pleased with my purchase.