I happened to acquire some third party SSDs made for 2013-2015 rMPBs (and 2012-2017 MBAs, I think, but I've never had one of those so I am less familiar). For the avoidance of doubt, all of these drives were made for the Apple 12+16 adapter, none of these is an M.2 NVME drive with an adapter.
I've had a lot of success scoring low-priced drives on eBay, Mercari, Offerup, etc. I know there's a risk with second-hand equipment, but if you're smart about it, my experience is I can find super low-cost stuff for very little money. I recently got a (new) 512GB OWC X2 drive, along with OWC Envoy Pro enclosure, for $36 (plus tax, plus shipping) on eBay. OWC charges $229 for that, retail. If I manage to pick off a Fledging Feather cheap, I'll add it to these results. Point is, by picking off super low cost opportunities, I think I more than mitigate possible issues with scummy sellers.
I ran Amorphous Disk Mark 4.0 on combos of OWC Aura N2, OWC Pro X2 and Apollo S3 (all 1TB) with a rMPB11,5 (mid-2015, with I7-4980HQ processor and discrete graphics). For completeness, I also tested an SM0512F (Samsung SSUAX, MZ-JPU512x) and SM0512G (Samsung SSUBX, MZ-JPV512x), each of which are obviously 512GB.
TL; DR - OWC N2 and Apollo S3 are way faster than SM0512F, reads aren't as fast as SM0512G but writes are. X2 outclasses them all, but theoretically, the rMBP11,5 is capable of PCIe3.0x4 speeds which are something like 3500 MB/s, so you can see I've got some headroom.
The OWC Pro X2 is the "fast" OWC replacement SSD. The N2 is their more basic version. The Apollo S3 is a more recent entrant into the replacement drive sweepstakes from Mobile Sentrix. The SM0512F is the generation of Apple drive supplied with 2013/2014 rMBPs (and other contemporaneous Macs). The SM0512G was supplied with 2015 rMPBs. I have links to descriptions below.
One thing I found a bit odd is that write speeds were faster than read for a lot of these.
I think everything was done on Big Sur, but one of them may have been on Monterey.
Apple SSD SM0512F drive (so-called Generation 3 in this Beetstech description):
beetstech.com
Apple SSD SM0512G drive (so-called Generation 4):
beetstech.com
Apollo S3 (look at the info for the S3):
www.mobilesentrix.com
OWC Aura N2:
eshop.macsales.com
OWC Aura Pro X2:
eshop.macsales.com
Results:
I've had a lot of success scoring low-priced drives on eBay, Mercari, Offerup, etc. I know there's a risk with second-hand equipment, but if you're smart about it, my experience is I can find super low-cost stuff for very little money. I recently got a (new) 512GB OWC X2 drive, along with OWC Envoy Pro enclosure, for $36 (plus tax, plus shipping) on eBay. OWC charges $229 for that, retail. If I manage to pick off a Fledging Feather cheap, I'll add it to these results. Point is, by picking off super low cost opportunities, I think I more than mitigate possible issues with scummy sellers.
I ran Amorphous Disk Mark 4.0 on combos of OWC Aura N2, OWC Pro X2 and Apollo S3 (all 1TB) with a rMPB11,5 (mid-2015, with I7-4980HQ processor and discrete graphics). For completeness, I also tested an SM0512F (Samsung SSUAX, MZ-JPU512x) and SM0512G (Samsung SSUBX, MZ-JPV512x), each of which are obviously 512GB.
TL; DR - OWC N2 and Apollo S3 are way faster than SM0512F, reads aren't as fast as SM0512G but writes are. X2 outclasses them all, but theoretically, the rMBP11,5 is capable of PCIe3.0x4 speeds which are something like 3500 MB/s, so you can see I've got some headroom.
The OWC Pro X2 is the "fast" OWC replacement SSD. The N2 is their more basic version. The Apollo S3 is a more recent entrant into the replacement drive sweepstakes from Mobile Sentrix. The SM0512F is the generation of Apple drive supplied with 2013/2014 rMBPs (and other contemporaneous Macs). The SM0512G was supplied with 2015 rMPBs. I have links to descriptions below.
One thing I found a bit odd is that write speeds were faster than read for a lot of these.
I think everything was done on Big Sur, but one of them may have been on Monterey.
Apple SSD SM0512F drive (so-called Generation 3 in this Beetstech description):

Apple Proprietary SSDs: Ultimate Guide to Specs & Upgrades | BeetsBlog
Apple’s SSDs are confusing. Are they M.2 drives? What connector do they use? AHCI or NVMe? What drive can I use to upgrade? We have answers. We’ll tell which SSDs work in which MacBook Pros, iMacs, Mac minis and more.

Apple SSD SM0512G drive (so-called Generation 4):

Apple Proprietary SSDs: Ultimate Guide to Specs & Upgrades | BeetsBlog
Apple’s SSDs are confusing. Are they M.2 drives? What connector do they use? AHCI or NVMe? What drive can I use to upgrade? We have answers. We’ll tell which SSDs work in which MacBook Pros, iMacs, Mac minis and more.

Apollo S3 (look at the info for the S3):
Apollo Solid State Drive for Macbook | Macbook Replacement Parts
Mobilesentrix offers best quality Apollo Solid State Drive for Macbook, Macbook Air, Macbook Pro, iMac, Mac Mini. Find more Macbook Replacement Parts.
OWC Aura N2:
OWC Aura N2 1.0TB SSD for select 2013 and later Macs
SSD Upgrade (Blade Only) for MacBook Air (Mid 2013 - 2017), MacBook Pro (Retina, Late 2013 - Mid 2015), and Mac mini (2014). 3 Year OWC Limited Warranty.

OWC Aura Pro X2:
OWC Aura Pro X2 1.0TB SSD (Blade Only)
High performance NVMe flash upgrade for 2013 and later MacBook Air, MacBook Pro, and Mac Pro computers. Get speeds on par with the latest Mac models.

Results: