Just a hand full of years ago, I purchased from FiveO Motorsports 4 x 750cc Siemens. That was maybe 10K miles ago.
At around 2-3K miles ago, the engine began to hesitate and buck @ steady low RPM between 8-12 inHG vacumm.
In the attempt to isolate the culprit, I sent them out to WitchHunter Performance to be serviced.
Their flow rates after service were all over the place!! From low 700's to low 740's. I didn't know what to believe.

Now I'm in the process of ditching the stock ECU for a standalone.
I'm considering 750's x 1400-1600's although have been suggested to go with 4 x ID1050's. Not crazy about the idea of a 1050 on the primary.

Not a lot of performance injectors sites out there that I can find. I'm reluctant to buy from FiveO Motorsports.
They offer a "Black-Ops M-Series" but can't figure out where/who makes them? They appear to be a FiveO Motorsports only injector.

Is any1 running/purchased injectors from this site?
4x 1400cc for MAZDA OEM 04-08 RX8 RX7 13B Miata fit Denso yellow fuel — KSM Motorsports Limited (ksm-motorsports.com)

Excellent standing with EBay. They are locate in the island of Cypress surrounded by some of the most unstable countries on this planet!

 

I just buy genuine Bosch parts and whatever tophat/seat combo I'll need for a given rail setup. FiveO has had a few bits of shade thrown at them for potentially using either full on knock off or poor post process on their injectors IIRC.

 

this is all the red flag you need to stay away from that website. the price is also a dead giveaway.

injector technology has come a long way. a 1050 on the primary will run and idle like stock with proper tuning. fear not. an id1050 primary with whatever larger size secondary you want will be perfect. it really comes down to your boost/power level what size secondary to go with. 4x1050 may work but it really depends on your set up.

 

^What he said. Just buy the appropriate sized Injector Dynamics (ID) injectors for your build/power requirements. Best thing about those is the data ID provides for the injectors (i.e., flow, dead time data, etc.) is dead accurate, so you'll have a much easier time tuning with your ECU - takes away lots of guess work. As for sources to buy them from, I like Banzai Racing - he won't BS you on availability, charges a fair & competitive price and you'll get them pretty quickly.