I beleive that the flat rate is not accurate as you mentioned, but the EMI is not up to 11%.
I have expereince with the Qatar Islamic Bank, which announced the rate of 4.12% for the first year. I have purchased the car through them and at the end it's 5.8%, which I consider a ver attractive rate . In additition to that the car is in my name TOTALLY . I don't have to wait till the payment is complete.
They have finished the documents in 15 minutes and every thing is wonderful.
At the same time I have visited the QNB for the same purpose, that claimed that they offer 3.99% and after calculations, it was 8.5%.

I advise everyone to calculate the actual amount he/she pays and see what is the real rate.
good luck everyone.