The Groupees Doujin Bundle is an odd little collection with a few outstanding highlights. The $1 (60p) tier includes Qualia 3, Akane the Kuniochi, dUpLicity and some bonus content, but the $4 (£2.50) tier is the one to go for. It adds Danmaku Unlimited 2, BlazBlue: Calamity Trigger and RefleX to the mix, all of which retail for between £3.99-£6.99 apiece on Steam.
A niche proposition, then, but a doozy if you're in the market. RefleX is still an absolute corker.