I have tried a free sample of Mitragynine isolate. It was a sandy brown/reddish powder.

70mg was all I had so I took it at once, and it gave some pretty good sedation, comparable to a low dose of Oxy. (Not really into opiates though.) It was too expensive per dose for me to pay for it though, I'll just stick to bali leaf.
Also I wouldn't have minded dosing higher, or combining it with kratom leaf. I haven't tried the latter but have read good things!

Any other Mitragynine experiences?

7 hydroxy and 7 acetoxy or soemthing - wasnt as nice as streight up kratom imho
home extracted yellow powder - very nice - very.

I have dabbled a bit in kratom extracts...(not making them, just eating them)

I prefer the regular powdered leaf. It seem to not build a tolerance at all whereas the extracts and isolates seem to build a tolerance quickly for me.

It may be because its easier to overrdo the extracts. I take 6 regular powdered Kratom capsules...thats allot to swallow... takes time to cap them up (even with a cap machine) Usually, if it doesn't kick in, I wait it out and it comes on fine. With extracts, I only need a cap or two...so I guess maybe I am a little more quick to take another cap when its kicking in slow.

I drank some Kratom extract tea once. It was really calming and slightly sedating.