I see one of these has turned up in the UK. Are there only 90 in existence…?
Darn. I’d bag that if I had the cash. 
I had the chance to purchase a Soundplane on Reverb during the time I was also considering the LinnStrument. In the end, I chose the LinnStrument because it is USB class-compliant with Linux, whereas the Linux client for the Soundplane was not available at the time. Looking back now, I made the correct decision since the situation has not changed.
as I’ve mentioned previously, I think the Linnstrument is more accessible/useful for the majority, its very much plug n’ play, a reliable playing isomorphic surface for melodies.
the soundplane is very different… it excels as a multi touch expressive surface.
whilst many happily use it as a melodic surface (its fantastic with Aalto) , and I will also say, the Soundplane also looks beautiful and the feel of the wood to touch is an absolute pleasure.
but for me, its strengths lie elsewhere (compared to linnstrument), where you want to use its entire surface … as its surface is fully continuous in the X/Y planes (which the linnstrument is not).
so if you want to ‘just’ play out of the box synths using an expressive surface… Linnstrument,
but if you are more experimental, perhaps like creating instruments / experiences (in say Max/MSP) , the Soundplane rocks - but its a pretty niche use-case 
(
but hey, the fact we have the choice, is the most important part… different musicians need different things.
notes:
a) Soundplane linux compatibility, thats been possible for quite a while now ( 8 years?), Ive used it on a few projects/platforms… but you need to be a developer really to make use of it.
b) I’d actually say the Erae Touch is a closer ‘competitor’ to the Soundplane (than the Linnstrument) esp. in this experimental area… as its has a user api to use.
its advantage is you can program the leds for feedback which is very useful, and I think form factor is slightly better (larger in the Y dimension)
however, its no where near as as nice to play as the Soundplane, nor as sensitive.
(and as you can read in this forum, and elsewhere, the Erae Touch has firmware issues)
but again, depending on use-case, one might be more suited than the other.
That may be so for the majority, but it was not for me. I come from a piano/keyboard background, so the 4th Strings layout, along with every other layout, has no relevance. I decided on the tritone layout because of my jazz background, and because it heavily simplifies memorization of the playing surface.
Then I spent several months writing documents for the tritone layout and how to use it. Unlike the 4th Strings layout, there are very little, if any, resources for the tritone layout.
Lastly, the grid playing surface and Braille-sized bumps across it constantly disrupted my performances, so I had to modify my LinnStrument so that the playing surface is flat.
I chose the LinnStrument as the replacement controller for the piano/keyboard, so playing harmonies and melodies proficiently/simultaneously is my minimum bar. I swore a vow to never play the piano/keyboard, except to demonstrate and explain its physical limitations, so I am open to all alternative controller layouts, subject to my gratis and libre open-source software criteria.
Yes, I am aware there are build instructions for the Linux client, but that is not user-friendly. I suppose I should be grateful they exist though, considering the development of the Windows client has stalled.