How do you find your KX3? I was going to get the K3, but they discontinued them for the K3S but that went up £500! so didn't bother.
I might get a KX3 for Field work, do you use it QRP or with an amp?
Note that Elecraft sells the PowerWerx supplies these days from their website. I don't know if that's a practical way to get one in the UK, though -- I can imagine that shipping and taxes might make it a poor value, if it's possible at all.
Since I built my 50W amp (Hardrock-50), I use my KX3 mostly with the amp. But I have used it by itself plenty in the past, and will do so again in the future for portable operation. The amp is reasonably portable and lightweight, but when you combine it with the batteries to supply it for any length of time, it starts getting tempting to leave the amp behind for portable use. Elecraft sells their KXPA100, which is twice the power of my amp, but it's also twice the weight, twice the volume, and about twice the price. It is better integrated, but the combination I have is easy enough to use.
The KX3 is my primary HF rig, both for home and portable use. Its receiver is outstanding, with great adjustable filtering, very good ergonomics, and lots of nice features built in. I've owned it for a couple of years, and I've used friends' rigs by the major makers, but I haven't found another radio I'd prefer overall. The only significant shortcoming of the KX3 is that there are times when I want more power, but an add-on amp takes care of that. It's amazing that they pack that much radio into such a small box.
I'm afraid we might be drifting a bit off topic for this board, but if you want to dive deep into ham radio discussions, feel free to look me up on qrz.com, and send me an e-mail there, or start a thread on one of the forums there.