Memrise

Memrise.com is also a wonderful place to learn Irish. It also uses a quizzes type of system to help you learn. The difference is that anyone can make a course on Memrise which means they may or may not be correct. I would suggest if you find a course with an error in it on memrise that you inform them of the error and then leave the course. Irish is difficult enough without learning it wrong to begin with.
There are a lot of Irish courses to choose from on Memrise. There is even a Duolingo course which will definitely help you with Duolingo. But there are also specific courses like ones on the Days and Months in Irish (which I cannot seem to learn well from Duolingo), the weather, numbers, adjectives, question words etc. etc.
 Memrise also has courses to go along with Irish language books you may have like Learning Irish and Gaeilge Gan Stro.
Memrise also tries to encourage you to come daily with a "streak" clock. I basically ignore the thing because I have so many courses going on there that I could never keep up with them all every day.
They also have a Pro version that you can pay for which adds a few nice features. I pay $7 a month and am happy with what I get for that.
If you have the time I would suggest using Duolingo and Memrise together. You will learn a lot more. I usually stay on Duolingo as long as I can and then when I get sick of it, I go to Memrise where the learning is not quite so intense for me.