From your OP link
Both are master units that can program the other units.
-The tradeoff: No battery backup in loss of power / if unplugged
-The BSM7 can continue to download when not plugged in
Which is really minor. Our club hasn't upgraded because there has been no need, BSM7 is still probably the right choice.
Think I will check SI-Droid out too out of curiosity, I don't really follow the desire to not have a laptop at events with all the other SI equipment you bring anyways. But would be neat to run event on a cheap Chromebook as I believe they can run android apps now, and be able to have easy option to output live results.