Re: BTCJam how secure it is?

You can have a look at our stats page to see the returns that are possible: https://btcjam.com/stats

How is the "total investor return" stat calculated?
I can see the investor return for A-rating bitcoin loans is 29%, so is it that the lenders can get 29% profit on average from each of the A-rating loan?

If you invested in all the loans since Jan 1st 2014 that were A rated, you would have made 29% ROI on your money (that is of course only on the money that was due until today, parts of those are still outstanding)

does that also include all the a rated scammers, or just the ones that paid back their loans?

The returns shown here are net of defaults. So even if someone is 1 day late, the calculation will show this as a 'loss'