Node 2i interface/app, a beginner's question

I know almost *nothing* about the Node 2i and have a pretty basic question. My teenage son has a decent first-time stereo in his room, and he uses Spotify on his phone connected to the receiver via an RCA/headphone jack cable. It's awkward to use and he has no way to play files from a flash drive, internet radio, etc. 

I'm thinking of picking up a Node 2i for him. It looks like he can run it remotely from his phone, connect a flash drive, play internet radio, and likely have improved sound quality.

My question is about the phone app. He's used to the Spotify design and I'm not sure what the Bluesound app is like to use. (I'm assuming that he has to use the app as a remote, not the Spotify app.) I know it can stream Spotify but I can't tell beyond that whether it's an intuitive, appealing app. The reviews at the Apple store are discouraging. Does anyone have any thoughts? Any experiences going from the Spotify app to the Bluesound app? And, since I'm asking questions, is it easy to run Roon on the Node 2i? (I've never used Roon but I've looked at the website a bunch.)

Also, respectfully, I'm not interested in considering other streamers unless they're at or below the Bluesound price. He cares less about audiophile sound quality; he just enjoys music. I want something easy and well made.

If he doesn't really care about audiophile sound quality, just get a quality bluetooth receiver, like the Auris BluMe HD. I use one in my system. You simple pair it with your phone or laptop and stream whatever. I stream Spotify Premium, YouTube, Radio Paradise and other internet radio stations.

I think the Auris BlueMe HD costs about $120. It is the best bluetooth receiver I've used. Really good range/connectivity and the sound quality is surprising good for Bluetooth. Just buy it direct from Auris on their website. Free shipping and same price as everywhere else.
If you or you son know anything about computers an inexpensive way to stream is with a raspberry pi4 connected by ethernet and then to your preamp. There are different ways of doing it but controlling it by phone or tablet is pretty easy. Here's a link to a few music streaming OS's that can be used.
He can still use Spotify as a separate app. It will automatically work through BluOS to control the Node2i. Just choose the Node 2i under devices available. At least that’s how iPad and Spotify premium work.  Not sure if you still need Android/ iOS phone.
Thank you all so much for your responses, which are helpful and encouraging. One reason that I'm interested in the Node2i is that he can connect a flash player with music files. 

Again, thank you!
The Node2i is super easy to set up, sounds fantastic. The app works very well on my iPhone though I’m still getting used to the layout.  The headphone amp inside is very good which might be an added bonus for you son. Quality product. No brainer if the 550 price point is not an issue.  
The Bluesound app is excellent and super easy to use.  The only way to play Spotify (that I'm aware of) with the Bluesound is with the Spotify app.  You'll see "Devices Available" or a small icon in the bottom left corner of the Spotify app.  Click on it and you can select the Bluesound to stream to.
The Bluesound app works with the Spotify app independently.
Your son will open the Bluesound app, then the Spotify app.
From the Spotify app, choose the speakers. 
All music he/she wants to play will be on Spotify, but will go through the Bluesound app.
It works pretty nice and Bluesound offers a lot of other services (like Amazon, Qobuz, and Tidal).
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