The main thing I like about them is that they are very flexible because of their open source community approach - it's amazing how much support you can get from other users! Sometimes when using some features there could be delays between actions so this would make us feel confused at times but overall was fine as long we had patience :) Would recommend anyone with questions or doubts just go for any one who will help out by providing answers (even if its free).
We mainly use tigerbay due our eCommerce website needs customization options where customers have an option not only pay online through credit cards etc., also give discounts/coupons via emails which sometimes doesn't work properly hence need manual intervention otherwise everything works nicely well integrated into site without issues.