I have YLM m400+ (ess) and iFi Gryphon. I like the sound of YLM more, where, in my opinion, more interesting, denser and more structured bass, more melodic middle frequencies, the resolution in general is at the same level. Gryphon sounds less emotional, harsher, more rhythmic, electronic music sounds better on it, instrumental and vocal music sounds better on m400. The Gryphon is also much less noisy, especially noticeable with low-impedance headphones.
The Gryphon's Bluetooth LDAC sounds a lot better than the m400's aptX. The Gryphon connects well to a computer, I always had problems connecting to windows with the m400+ and this is a good reason for me to keep the Gryphon.
The workmanship of the Gryphon is much better, clearer working buttons, I have problems with them in the m400. I haven't seen the insides of the Gryphon, but I have had to open the m400 and inside it looks like the work of an enthusiast. The Gryphon has a large informative display, with several LEDs to help you quickly navigate the settings. The Gryphon also has more sound settings, but I'm not used to them yet, constantly going back to the sound without modification. Despite the fact that the m400 warms up a lot when in use, its battery lasts longer and I never had to stop listening to the m400 because of the battery, with the Gryphon I already managed to get into this situation. Also don't get your hopes up for YLM support, I've contacted it a couple of times with no result.