I have a 6 Brothers folding board and 6 Brothers glass bi-convex stones I use as my primary portable set. The board is slightly smaller than standard (37cm x 37cm) and the grid is square not slightly rectangular. You have to use 20mm stones. Regular 23mm stones are too large for the grid. I enjoy not having to lug around a full-sized go board, yet it is still comfortably playable. I bought the board and stones at separate times (board originally came with cheap plastic polyethylene stones) I believe the folding board was about $60 USD, and the glass stones and plastic bowls I found for about $35 USD. I bought both on ebay.
