I've owned a bunch of them. Fireballs, 60 and 100, invader, savage, artist, steve morse. I like the artist the best.
The build quality is hella sus. I know a bunch of reputable techs that will not even touch them, for any price.
That said, they have a sound. It's not my sound, but I love certain ENGL tones - Kai Hansen's gamma ray stuff comes to mind. Dude always had KILLER tones. Everytime i hear that intro to "men martians and machines" it's a reminder.
The only engl amp i would actually consider buying is the e530 pre, to scratch that kai hansen and necrophagist itch - but tbh the larry scratches all the itches the actual heads scratch and like 48 more.
They do sound okay, but those tiny, thin PCBs(look at them compared to an SLO or VHT/Fryette) and tiny transformers will keep me from ever risking owning one again. I have too many friends with too many horror stories...... and I dont know anyone who will actually work on them if something goes wrong.