I’ve the RS150 streamer DAC, for sound quality it’s tough to beat, a local so-cal Hifi store uses it exclusively to demo high end equipment.
I also love the video integration to a monitor, so you can stream and play not just audio but videos too.
the app I find most of the time to not be an issue, albeit there are times my iPad seems to not want to connect which can be frustrating. It usually straightens out, ironically if I use the app on my iPhone it seems to be no problem so could be an iPad issue. Only difference between the 150 and 151 is an updated DAC, which I don’t think is a huge deal. Consequently you can get pretty good deals on used if you like. Build quality is stunning, it’s beautiful.