This is interesting on a lot of levels.

Why the conversion rate has changed so radically is a subject for conjecture at best.

If only a month, there are few rebills, I am assuming a monthly subscription and not rebills like our cam sites do. You mean conversions from free trials ( or $3 [whatever])?

What your chargebacks (and disputed transactions) will be a few months down the road remains to be determined. With your own merchant account you can not only dispute chargebacks but also institute your own loss control processes at the transaction-point (the "buy page').

I don't think the volume matters that much -- any profit is a good profit. But it is only a profit when you deduct your time spent in administering your own merchant account and the billing process.

Like I said in the beginning "This is interesting on a lot of levels."