I have not seen any reviews of the not topspin and twintwist but have heard that for the price, they are pretty good. Plastic quality is similar to the MMC Screamer but the plastic is thicker and feels better in-hand. Listen to TFW 2005 and Radio Free Cybertron latest podcasts. Both have someone who purchased and were pretty pleased. I have been thinking of dropping the cash down myself.
They seem to have great articulation while staying true to the G1 looks. For 3rd party, they are very reasonable in price compared to what is currently available. About the same size as a current deluxe figure. Good luck if you get it. Would love to hear your thoughts on them