I own the KT88 Fierebottle amp by Dennis Had. I have had a blast with it but I am a bit of an odd fish to say the least. My system sounds amazing with it but for me being able to try different tubes is a big draw. I love the tubes themselves and I enjoy hearing how they sound. Output tubes I've used so far include KT88, 7189A, KT66, El38, 6ar6, 807, and 6v6. I've used 6bx7, 6sn7, and 6sl7 in the input plus loctal versions of this and the 6v6. Lots of fun. But I do understand how that could be frustrating for some people.
In my system (Topping D90, Supratek Cabernet, KT88 Firebottle, Phase Technology PC 3.5 speakers) I can get a variety of different sounds depending on what tubes I use. I'm currently using a pair of 7c5 tubes in the output and a tall 7n7 for the input. It's a. big, warmish sound. I can go very hi-fi if I put in the new KT66 with a Raytheon 6f8g. I love being able to change the sound of the system. It isn't a purist approach but a SEP will never appeal to the 100% accuracy crowd.