Yes, but for some reason lined fretlesses are popular. It seems strange, you hardly ever see training wheels on bicycles, but manufacturers make most fretlesses lined, and when you're buying a custom bass second-hand you don't get to specify it.
AFAIK, no and no. Neither Tonelib-Zoom nor (as far as I can make out) Zoom's own GuitarLab will control either the B6 or B2-Four, either on Windows or Android. Zoom seem obsessed with iOS to the exclusion of all else.
I'm not sure as I haven't used any effects which use the "control switch" (there are a few others), but I can only think that the footswitch for the effect doesn't switch the effect entirely on or off but just controls the relevant parameters.
They have less markup as Thomann owns HB so they can sell them at cost if they want without making a loss, then flog you all the accessories for a profit.
OK. All I have to do is upgrade the vocal-only PA so it'll take bass too, find somewhere to store the active sub and employ a slave to move it, mic up the drums, and either mic up the guitar amps or persuade the guitarists to go through the PA. A couple of thousand quid and an extra hour of setting up per night should cover it.
https://yoshblog.com/en/review/b2-four/
From looking over the various reviews of the B2 Four, buyers seem to be very happy with it. There's a very detailed 4* review at Amazon.com that's worth looking at - https://www.amazon.com/product-reviews/B0BW6BSPLV/ref=cm_cr_unknown?ie=UTF8&filterByStar=four_star&reviewerType=all_reviews&pageNumber=1#reviews-filter-bar
Haven't played with a 5-piece since 2010 except for one dep gig with them in 2016, just consulted photos and I was second row on the drummer's right, one side or the other of the rhythm guitarist. Although now my smart-alec answer would be "I don't, I sit down".
Fretlesses also have markers, whether they're lined or unlined. Go figure.
I prefer unlined but I'd rather have my lined fretless Sei than no fretless Sei.
This is something I've been complaining about ever since the Zoom MS-100BT which only had an iOS app. Zoom are ignoring the majority of smartphones and tablets.
Tonelib doesn't support the B6 or B2-Four yet and there doesn't seem to be any response from them on the subject - they're a commercial operation and Tonelib-Zoom is freeware so they might not feel any great impetus to update it. Zoom GuitarLab was last updated in 2022. I think Zoom have just lost a sale.
Also listed at Thomann: https://www.thomann.de/gb/zoom_multi_stomp_ms_60b_590550.htm - £138 plus a tenner shipping, availability listed as "on request".
The Bax listing now says "Delivery within approx 15 workdays" and it's down to £135.
Are you looking for a set and forget type or do you want multiple patches for assorted sounds?
What is "not too expensive"?
Have you had a look at the Zoom B2-Four? Similar capabilities to the B6, not as many switches and no touch screen but half the price.
If your eyesight is as blurry as mine, check resistor and capacitor values before putting them in. Something like https://www.ebay.co.uk/itm/166388291985 is really useful.
I always use one except when I'm using the Nux Mighty Plug. Leads just get in the way. With bug-type wirelesses, it's hardly any more onerous than plugging a lead in.