I had compared almost all the brands before buying Zeven - SPI, Dr. Kong, LEGO... Zeven is the lightest and has back support. The size, even the smaller one, looks big for 6 year old kid but it is ok.
They have shops in Ocean Terminal, Lee Garden II and Elements at Kowloon Station. The new batches arrived in May and a few popular designs sold out already. The sales said the best time to buy in May / Jun - if for more choices. Most of the items are sold out before summer.
Price is around $900 but can use at least 2 years (had used for 2 years but still ok). We put in the washing machine every 2-3 weeks.