I've just taken a chance and ordered this card from AliExpress for some stop-gap upgrades to my 4,1:
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
The Ableconn is tempting but I really want to support 4 blades without spending Highpoint money while I stretch out my 4,1's usage and the current offer makes this card a similar price to the Ableconn. The ADWITS (and white labels) is a non-starter IMHO;
This card:
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
is coming up on ebay (in the UK) under various brands at c.£200 upwards but appears to also need a SATA power cable:
Pour port PCIe 3.0 ou plus en 16x. Compatibles avec les tailles de SSD M2 2280. Visserie fournie.
www.ebay.co.uk
Find many great new & used options and get the best deals for NEW! MicroConnect MC-PCIE-ASM2824-X4 PCIe x16 to X4X4 M.2 NVMe SSD at the best online prices at eBay! Free delivery for many products!
www.ebay.co.uk
Will report back once it's received and installed.
I have an odd mix of SSDs currently... an old OWC 3.5" 480GB SATA2 SSD filling one of the drive bays; a Kingston Predator 240GB AHCI and a 970 Pro. Planning on a larger 970 Pro for my primary drive, repurposing the existing 970 Pro for Windows and installing a pair of something in RAID0 for use as a scratch disk. Hopefully some 1,1-3,1 users will be temped by the OWC and Predator when I put them on eBay...