It certainly is but the problem is that BetOnMarkets provides "digital options". Digital coming from the fact that when the bet expires, it finishes at 0 or 1.
What you are assuming here is that your bet will win. There are 2 ways the bet will go:
(1) Bet £6 and win £9 - great stuff - a 50% return
(2) Bet £6 and lose £6 - oh dear - a 100% loss
Please don't get carried away Mr Options, it isn't a cash cow. Regent Markets (BOM's parent company) make a hefty profit each year, and they don't do this by giving their money away.
Also, over the years, they have continually moved the goalposts when punters have been winning.
They aren't stupid....