It's discouraging to even try since you have to continue to discard dangerous tiles including all fours, fives, and sixes, along with the winds and dragons. It's like calling riichi without the benefits.
I had a shot at it tonight as dealer, and it was nerve-wracking up until West tossed a

I even tossed a red five as my first discard, something I never do.
No riichi, no ippatsu, no pinfu, no iipeiko, no sanshoku, and no tsumo. Just 2 han. I ran across this quote by HotelFSR from back in 2009.
"Players get Junchan less than 1% of the time, and it is impossible to stack with Tanyao and difficult to stack with pretty much anything else. The probablity of a stacked Junchan is tiny, something like 0.1%."
At least now it has its own thread.