The price difference is only $250, and I am in indecision. I think I will mostly roast 1 lb at a time, so M6 should be more than enough for that. But I could buy M10 as well, just in case.
Is there a difference in getting good roasting profiles? The most important is what I get in the cup. Also, sometimes I roast only 1/2 lb. I guess both M6 andM10 are capable of doing that, right?
Also, it is possible that M10 is more powerful, which could be important for better PID roasting, but I am not sure.
Any advice will be appreciated.
Thank you!

I just got an M10. Given the relatively small price difference, I'd error on the side of 'future proofing' your purchase.

The m10 can do 300g to 1.2KG. I like the flexibility

I missed this or I would have responded earlier.

I'd definitely get the M10 if you have the money. $250 is minimal when compared to total and it will give you much more flexibility. All the way up to a small roasting business if you really enjoy what you're doing and want to go that route. I have an M10 and really do like it, as the other poster said, it can roast a wide range of weights. I've gone down to as low as 250g and it worked well, just have to be careful since you'll hit FC in 2 minutes if you don't keep the power down.

Finally, my M10 arrived a few days ago. I like it. Before I used Hottop for several years, and Kaleido is so much better and it is so powerful. I can do anything. I did a few roasts, ruined a couple of the first ones, and now I am enjoying everything.

My next step will be to learn how to autoroast with the PID control, regretfully, there are just a few posts/videos about it. The PID parameters in the Kaliedo profile are 15, 0.07 and 0.06. Is it the right choice?

Thank you.