I think it's fine in a pinch and I've certainly heard SS amps that are worse, but a good dedicated SS amp will pretty handily trounce it, as expected. Basically, I wouldn't buy the Lyr+ expecting it to be an end-game tube and SS amp in one, but rather a tube hybrid with an SS mode as a back-up (maybe while you wait for a replacement tube to come in the mail), which is pretty much how they advertise it.
It's kind of weird to me that it's such a heavily emphasized feature, even given a fancy marketing name, the "Fusion Architecture", because I basically consider SS mode ignorable. It's not like it hurts it being there, and it's still worth the $100 over the Lyr 3 with that stepped attenuator and motorized remote volume control, but yeah. SS mode is kind of throwaway.