No hands on experience with Linnstrument but from what I’ve read it’s got very similar capabilities to Roli stuff (5 expression dimensions). I’d guess the decision between those two would mainly come down to your preference between the grid and the traditional keys layout.
Pros for these devices: distinct expression control over multiple pads/keys, vibrato is natural and pleasant to perform, Roli keys let you slide over to any other key.
Cons: I can only speak to Roli but I find their surfaces have more friction than I’d like. Also they require more force than regular keyboard keys.
Touche shares many of the same expression possibilities but is also in its own sort of category. You could think of it as being able to control almost four mod wheels at once. “Almost” because the left and right shiftings are mutually exclusive, and the top and bottom ones are semi-connected (depending how close to the center you’re applying pressure).
Pros for Touche: You can be more accurate with expression as it’s a larger tool with adjustable firmness. You can do more expression-things at a time (with Roli it’s not really comfortable to do a manual vibrato and a forward slide at the same time, for example). There’s a really nice percussive/stab trick with Touche where you can have a patch that doesn’t sound unless Touche receives pressure, letting you simply hold down chords on your keyboard and just tap Touche to trigger all notes perfectly simultaneously - your position and pressure produce all kinds of expression but you don’t have the sloppiness of the individual note attacks coming at slightly different times.
Cons: There is, of course, no per-note expression. Depending on your setup it could be awkward live - you need USB to power it and a table to put it on. It’s small enough that giving it its own stand of some kind could be weird but it’s large enough that you probably won’t find room to just plonk it down on the surface of your keyboard controller.
Depending on what you’re trying to do Touche could really shine in conjunction with another expressive controller. For me it’s going to be taking over mod wheel duties wherever possible.
