I was getting close to pulling the trigger on a set of these M1 boost centerlock and it says plenty are in stock but they can't be shipped to the United States.

My 2 pair were ordered with an American credit card on AliExpress, but shipment was to my overwintering home in Thailand, duty free delivery.  Approaching 10K km on my oldest pair with original 36t stars and other internals, daily 40km rides include advanced climbs with 1Kw mid drive ebike.

...So all manufacturers have their issues I suppose.  Regardless of big OEM or Chinese clone.

Ouch!  Yeah, hard to foresee the many potential issues with a radically new design.  As I was building the Spirit 9 months ago, I saw a potential disaster leading to a frame fracture caused by the dropper cable getting in a pinch point with the belcrank arm on top of the shock.  I epoxied in a 3cm piece of carbon fishing rod to route the cable through.  On the bright side I was able to check the torque of the shock eyebolt easily with air set to run pressure.

How is the bike holding up?   Any updates after 3+ months of riding?...

I had been thinking that I need to post an update pretty soon on here as last week I began working through the local distributor about a newly discovered crack in the seat tube, about 5cm below where the top tube joins.  Two days ago I was informed the manufacturer would send me a new main triangle for shipping cost and peacock paint upgrade cost, around USD50 total.  Best I can figure it was caused by insufficient strength of the wall of the seat tube.  Dropper post was deeply inserted so not related to being near minimum.  Dropper post seemed to fit OK diameter wise too.  I took them up on their offer but I'll relegating the bike to my wife to use (after replacing main triangle) as she is much lighter and gentler on stuff than me, and she likes the bike as did I.  In summary, I rode the bike every morning, 32-36km, 50/50 trail and asphalt for over 9 months, so over 7,500km.  I had planned to convert it with the way lighter Photon drive but then got spooked off of that drive as longer term expert reviews began to appear.  I can tell you more about the experience after my new triangle arrives.  Ground clearance was right at 21.5cm unsagged, and clearance was never a problem for me but may be for others who ride more extreme.  A week or two before I noticed the frame crack, I had began a new build for my son, it is reviewed under metal frames on this forum.  I was hoping manufacturer would have offered the choice of a partial refund and I would have built another one of the alloy ones, it is less than half the price.

Either I could not find it, or this frame recently appeared on AliExpress.  I think it is assembled by the F. Yuzhe/Twitter conglomerate, or possibly only marketed by them.  I needed a sturdy, modern, and economical  ebike donor frame for friends and family to use when they visit me in Thailand.  Some particulars:  I used a 100mm Bafang 1Kw motor on a 73mm  threaded BB, with 7.5mm DS spacer and 20mm NDS spacers to get a perfect chainline with a offset chainring and a 9s cassette converted to 10s cog spacing, rear triangle looks like it will easily take a 29 x 2.6 and likely a 27.5 x 2.8 tire, 65 degree head angle, rear travel up to 150mm with a longer optional shock--I set it up for 140 front and rear.   First 250km of full speed trail rides reveal a solid flex-free rear triangle and a confidence inspiring planted feeling front.  Finished weight with BBSHD and a 48v/17.5ah is 54.6 pounds.  Motor ground clearance 20.5cm. 

OK to go full Chinese components as well and I'd like to keep the weight down. What's a reasonable weight expectation and what should I focus on? I think I need about 130mm of travel.

Read some of the threads on here under the 29er frame heading, some highly capable and gorgeous bikes being built.  There is one in particular that makes a great converted ebike.

Yeah, I'm contemplating just buying some sheets and making it myself. It's just going to take some time. I'm trying to avoid that. There has to be a brand out there that some PFF company make a template for these bikes.

The frame I bought was a first release model, so no chance of a kit.  I could have maybe found a kit for a similar looking frame but opted to just buy 4 meters of 3M Rhinoskin.  It was a fussy task, as I doubled up in a few spots, but in the end it was 2 hours well spent.

you're right....maybe with some PU inner tube...

I don't find some reasonable wheels below 300€ in aliexpress, that weight less than 1900gr

I have had good luck with the following, some assembly required.  Ryet 29", 33mm outside width, assymetric carbon rims, USD175/pair, Ztto M1 36t ratchet hub, DT Swiss straight pull stainless steel spokes with copper nipples.  Price, if you can build them yourself, is around $325USD.  Spare parts for hubs are easily found and cheap.  4k km and no issues on one of my 1Kw ebikes, other pair recently installed.