For me, 'Steampunk' means, at its purest, works set in worlds where Babbage succeeded and electricity has been ignored and/or failed. However, being a form of 'punk' it spreads across time and genre-boundaries, not least because some authors wrote about the future before it happened, even in the 19th century.
Unfortunately, this 'Steampunk Megapack' isn't very good at being 'Steampunk'... the selection is poor, even for a budget title... you could put together as good a list by Googling "Steampunk". It looks like the editor(s) have cobbled this selection together without bothering to bother thinking much about it. For example, 'The Mid-Watch Tragedy', by Vincent Starrett, is a straight-forward sub-Agatha Christie murder-mystery set on a trans-Atlantic liner that (wait for it) has steam engines.
However, it is a mixed bag, and it's only 31p. It may not be Steampunk, but I was glad to discover 'The Machine Stops' by E. M. Forster (which is his version of 'Brave New World'). As a rule of thumb, I found the editors of this collection were honest enough to detail the contents; don't buy it as an "Introduction to Steampunk" but if you've got 31p spare, you could do worse than buy it for some bloody-good stories (with the bonus of trying to work out what they have in common).
Good luck on that last one... ;)