The TMC box is a little more sophisticated when compared to the Bluespark and there is a dedicated TMC Euro 6 box available. But both offer and deliver essentially the same results.
I have not tried TMC Box so cannot comment but the Bluespark I have is brilliant, absolutely worth every penny. Power and fuel economy has increased, works in 5 settings and noticeably too. Mine has been set on E a week after I got it, not any problems at all.
300+ for a tuning box is a little pricey for me, let's face it the A500 needed fiddling once and another for a Euro 6 version not that much R&D really. I"m not belittling the experience, skill or hard graft to make these boxes at all but 300 big ones? Probably if I had the spare I would have gone with TMC as I tend to go with labels