The J-2 and J-2000 both have the same internal parts so they will steam and perform the same. They both provide a continuous flow of steam. They are different only in the outward design and styling.
The J-2 is the older style, with a 1 gallon water bottle that sits up on back of the steamer. This tall 1 gallon bottle will provide steam for about 2 hrs. Due to the size and tallness of this water bottle, there may be some sink faucets that it will not fit under, in which case it could be filled in a bath tub. The J-2 housing is a die cast metal.
The J-2000 is the newer style steamer in the residential line. This steamer has a 3 quart water caddy that fits down into the unit and fits more flush with the unit. This 3 quart caddy will provide steam for about 1 ½ hours. The size and shape of this water caddy makes it easier to fill up under most any sink faucet. The J-2000 housing is an engineered polymer plastic.