I use it on my android phone occasionally when I’m out and about and don’t want to carry my book around. It is an ok app, not super great, but convenient and the only one out there, so I use it.
It has all the hours as well as the Mass readings and a few other prayers. As for downsides, the formatting is ok, readable, but not at all pretty or good. You have no choice as to whether or not you use the Saints days, you are stuck with whatever they give you. Also, occasionally there are mistakes, yesterday they left out the intercessions.
Basically, I would recommend it for its convenience or travel or stuff like that, but it isn’t perfect, so I wouldn’t use it instead of an actual book.