I own both: a Zoom H4n Pro and the Spire Studio. In term of ease of use, the Spire Studio leaves the H4n Pro way behind. Both do a good job of recording, but the Spire is very intuitive and doesn't take a bunch of click wheel turns and pushes and forwarding through various menus to get where you want to be (like with the H4n Pro).
If you are willing to put in considerably more study and patience, the H4n Pro has more "adjustability" (for lack of a better word). You have a total of 4 tracks to work with (3 if one of them is stereo with the X/Y mics). The Spire Studio gives you 8 tracks. The Soundcheck feature makes it easy to balance your vocals or instruments. Simple mixing by just sliding the level and position of each track on the Spire.
I like the sound better with the built in condenser mic on the Spire than the X/Y mics on the H4n Pro. The Grace Design pre-amps on the Spire Studio sound better to me than those on the H4n Pro.
The H4n Pro has the advantage with being hand-held (something I've never done). Also with a data card for onboard storage. Transferring files from the Spire to an iPad or computer could not be easier... literally one click.
I work with a music partner who is 1,400 miles from me - we send Spire tracks back and forth with no fuss.
If I were looking at it again, I would not have bought the H4n Pro... I bought it before the Spire Studio was released. I have not used mine at all since getting the Spire.
It would take me the better part of a day to record 4 tracks on the H4n Pro (because of all the button pushes and wheel clicks). In less than 2 hours I can record 4 or more tracks on the Spire Studio and have those files on their way to my partner. I generally do acoustic guitar, bass, drums, and vocals. My partner adds piano, synthesizer, and electric guitar.
Easy. Really. I've added a bunch of SoundCloud files to that thread that was mentioned in another thread asking about the Spire Studio...
https://www.acousticguitarforum.com/...d.php?t=502715
Hope that helps.