Almost all the RO system out there are made by companies the put together OEM parts and slap a private label on the unit. As long as the units' specification is the same, and put together properly, there is nothing else to watch for. It is similar to the time when a PC manufactors are just people who put parts together. It is a no-brainer job, kind of....
However, associated with the purchase, it is important for the builder to stand behind the product and provide adequate support. This is where the brand is important. If the price is not an issue, try to get a RO unit from company that provides knowledgeable pre-sale AND friendly post-sale support.