I have bought this to play using headphones at home. At the end I couldn't justify the price for the function that I bought this device for.
Issues:
Left and right in headphone out seems to be reversed. Minor issue, but still.
Sound is not tube-like, at least not for me. I own old Laney Cub 8, it's as entry as it gets to tube amps and I was not excited by the Simplifier DLX compared to Cub8, although YouTube reviews did seem promising. Maybe it's my headphones - ATH M50x, but, anyway, it didn't work for me. I guess it's also important to mention that I play mostly clean, DLX might work if you play in overdrive more.
Quality - doesn't seem bullet proof. Don't get me wrong, it's solid, but it feels flimsier than than EHX / Strymon pedals that I own.
Good:
No noise - I have used with Thomann wall-wart PSU and had no noise issues, which I've seen reported in reviews occasionally.