Looking to 1×10 on CXer so will not be needing the left hand shifter and it makes sense to save a 100 odd grams by getting a brake only lever which can be had very cheap, are the cheapo Shimano R400 or Tektro RL340 any good?

they’re both OK in terms of being a brake lever and pullignt he right amount of cable for (road) discs, but the hood shapes are VERY different between those two models so you may want to go and fondle them and see which will best work with your right hand lever in terms of feel.

You can gut a left hand shifter to leave just the brake lever if you’re dedicated, not quite as light overall but better for feel 😉

What are you using on the right?

I’d be using 105 shifter(s)

These guys might have something that works. Review I read a while ago said it works a lot better if you have bigger hands as its easier to deal with the throw of the gear lever.

Gevenalle Cyclocross

I attempted this on one of my builds. In the end I just went for sram rival shifters as the mismatch hoods were unsurprisingly uncomfortable.
I used a tekro and an r600 on the left.

Take the weight penalty- it’s worth it for the comfort.

I’d be using 105 shifter

current model 5800s or older?

The hood shapes have varied massively over the years so need more specific answer, but the R400 lever is nothing like the current 5800 105 in terms of shape, reach or feel, nor is the RL340 to be honest.

I don’t think there is a single brake-only lever on the market that comes anywhere close to current Shimano STI shape at the moment, if it were me I’d put up with the weight or gut a (broken) shift lever.

One bonus feature of using the shifter version would be the possibility of wiring it to the dropper post you will eventually add 😛 .

Look at Cane Creek SCR5 levers as well, they may have a chunkier hood.

I found using a disconnected shifter is annoying, as you still end up pressing the gear lever then wondering why nothing happens…

Cheers, think I’ll just take the weight penalty then!

Cane Creek SCR5

also known as the Tektro R200/R100 (now discontinued under the Tektro brand), is pretty much a copy of an older Campag lever and again feels very different to Shimano offerings, but is a great match to Campag shifters.

I found using a disconnected shifter is annoying, as you still end up pressing the gear lever then wondering why nothing happens

Easy to solve either by locking out with a cable and adjuster so it doesn’t move, or if its a sacrificial lever you can lock it mechanically with a well placed screw/bolt (may need to drill and tap a small hole though) when you strip the shifter cuts out.

I did this with microshift levers as they have 2 paddles rather than the brake lever pivoting like shimano, easy to gut the left one of the 2 paddles