Do not buy this
Your review: it all seems nice, but the add on doesn't fit the basic module, the connectors are to big for the shelves, so the shelves of your add-on are 1/8 of an inch lower, as result none of your shelves will level. Global industries claims this is the way the items is designed and there is nothing they can do about it, so don't buy it!
Pros: It does work if you buy the connectors from Uline... they work perfectly!
Cons: it doesn't fit, who sells an add-on that doesn't fit the basic unit?