Apologies for necro-posting again - but I've been running both add ons listed here - KodiDisplayInfo (which uses web access to Kodi, but has far less advanced display functionality) and Kodisplay (which is the main topic of discussion here - but seems to be an internal add on only)
The advantage of KodisplayInfo using web access is that the SPI display and display code can be running on a small and cheap Pi Zero W or similar and SPI display, independent of your Kodi platform - which could be anything that supports LibreElec, CoreElec or Android Kodi I guess - and the Kodi device itself doesn't need to have SPI support and the code to drive SPI or similar displays.
The advantage of Kodisplay is that it has far, far more functionality and is far more extendible.
A question to those who know - is all the functionality available to an add-on, in Kodi status terms, available to an IP connected device via IP calls (JSON? http?) allowing an external device to be set-up as a comprehensive second display?
I've played with Frontvew+ on Windows on a little Windows tablet - and it also offers a lot of functionality - but doesn't quite do what I'd hoped.
(My aim is to have a bit more detail than the OpenVFD/LCDProc or similar displays - so PVR Channel logo and programme name, time elapsed/left bar graph for Live TV, Album art for Music - along with track number, track title and album title, time elapsed/left, movie name and art along with time elapsed/left etc. on a 2-3" display, possibly even something bigger like a DPI-connected Hyperpixel?)