I have been working with, and implented, both Stripe and Paymill. I agree with the article that the only time you would go with Paymill is simply if Stripe is not yet available (and in those cases you are probably better off with a local competitor).
Paymill is just a bad copy of Stripe in regards of technology, customer support, processes etc. One example of this is the ID verification process. Stripe has this automated and it takes minutes to complete. With Paymill we had to send copies of several different ID documents to different people and the process took weeks.
In our case Paymill approval process was indeed long (2 months?), but the ID verification part was quick and painless. They did require the originals via mail, but it's really not a big deal. The hold-up was with the bank and Paymill fell short in giving any idea of the ETA. They replied quickly, but didn't say anything at all. In fact, 4 or 5 weeks into the approval process, it all looked so bleak that we gave up on Paymill and applied to Braintree. These guys were far more responsive and approved us in a matter of days, but then they also took several weeks to "finalize the setup", so in the end it was a wash between them.
That said, between Braintree and Paymill, BT is certainly playing a catch-up. For one, they just recently dropped minimum monthly fee and switched to simple per-transaction fee structure. Also, their integration requires more work on the backend and overall feels less transparent and "heavier" that Paymill's.
In retrospect, Paymill is not bad at all, but it is not dramatically better than others either. They are all about the same.
I've had a much higher conversion rate with PayPal, even though I love stripe. It's annoying, because it's hard to do add-on payments with PayPal. Stripe is basically a dream to work with. But, if you don't have PP, you should -- but then once you do, it torques your conversion numbers per platform because people just see the PayPal button and click it. Suddenly 90% of your sales are through PP. The fact is: no one wants to type in their CC numbers and all that nonsense. Convenience factor is huge.
It's not sensical to choose one or the other over which YOU like more. You're in business to increase profits. If that means a PayPal button, so be it.
It's worse than being long. It's kafkian hell. In our case, our Paymill onboarding support contact disappeared for three weeks, then misplaced the physical copies of the documents. Three months later, with the banking approval process still on square one, I gave up and went with PayPal + Reference Transactions.
Paymill is just a bad copy of Stripe in regards of technology, customer support, processes etc. One example of this is the ID verification process. Stripe has this automated and it takes minutes to complete. With Paymill we had to send copies of several different ID documents to different people and the process took weeks.