I find BM's version very much aesthetically pleasing, old meets the new, modern technology meeting with antiquity of the past... Heaven in my eyes!
I have searched up the Matthews' version and I've searched most of the scans of BM's version of the theme. I find that the BM's version is much more old, antique-like and more sepia/dark in terms of artwork, there are a few scenes where it is bright, but nothing comes to mind at the moment, even the Sun card is more sepia, than light and bright.
Now for reading, it closely resembles the RWS symbolism and tradition, so i'm sure it won't be so hard for a beginner or intermediate to read with.
Whereas the Matthews version is... well, agreeably, much difficult to read with. Most of the minor cards are filled with machinery and only rarely does it have any humans in it. Also, in my opinion, it holds more on machinery, and said machinery is more "Advanced" than the other one, it's more shiny, new, bright, like the people of that time in the "future" BASED their generation, their clothing, their culture, on the steampunk genre, but with a more modern twist (hence the shiny, not antique looking machines).
Steampunk by BM: Sepia/Dark and more RWS traditional.
Steampunk by Matthews: Bright/Shiny and more difficult to read unless you spend enough time with it.
It's now a matter of what people would find more of a "connection" with, both of these decks are awesome and really insightful in their own ways,
I've seen the other two Steampunk decks and really had no interest in them.
Well, that's my own opinion of it.
I've already ordered both.
lol, kinda rambly and disorganized. Sorry.