Should I swap out the Formula C1s and SRAM X7/9 for SLX brakes and shifters/mech or try them?

If I take off the Formula / SRAM stuff immediately I can sell as new and just use my old Shimano kit. But if I try it then it will have to be sold secondhand.

Has SRAM stuff improved in the last 4 years since I had wobbly suicidal X9 mechs that threw themselves into the spokes with alarming regularity?

The sram/c1 aren’t really worth anything, for a reason. The C1 are utter garbage, with possibly the worst placement of a bleed port except for one literally under the band clamp.

Personally I’d swap your slx onto the bike. But fork out for new pads and cables, maybe give them a turbo bleed.

I bought a bike that came with X5 running gear and Avid brakes…. if I’d believed everything I read on here I would have been straight on the CRC website ordering Shimano equivalents before going out on it…. I decided to live dangerously and leave them on the bike, over a year later and still going strong, haven’t had to bleed the brakes or index the gears once.
Give them a go, you might be surprised.

Matchmaker clamps means that if I lose the brakes I need some clamps for the SRAM shifters…

Try it, the OEM kit is not worth much so see how it performs. (I have some nearly new SLX as it was worth a go but performance was awful)

For me whenever I look at a new bike it’s bars, post & saddle that are first upgrades.

For me whenever I look at a new bike it’s bars, post & saddle that are first upgrades.

This^ and I’d add grips, stem (for preferred length) and tyres to the list

does explain why I’ve always built from frame