Those "portable" systems can end up costing you much more in the long run. Especially when you can get a full-size system for not much more. The big myth is that full-size systems aren't portable and they are. I even attach mine to standard bathroom faucets, no plumbing work required.
Before buying an RO/DI unit, be sure you're googling the heck out of your vendor. There are a couple terrible companies out there that will take your money, send you low-quality equipment and never provide service on their claimed warranty.