Zoi,
I don't know about colon-section as done by Thai surgeons, but have some pretty intimate knowledge of our local SA GRS unit's efforts (a 3 stage op, with 'colo' being the 2nd big op).
1) it is VERY invasive compared to inversion, even when grafting from thigh or tummy area.
2) All girls I know seem to have some issue with a tummy bulge, maybe Juiemac can give her comment here?
Some very skinny older tg and one pretty young one also, have tummy bulge like being pregnant... the older one looks like 6 –7 month pregnant, the younger one, 3 – 4 month like.
3) You mentioned the smell, and yes, that is an issue and it may take some more or less long time to stop. It's NOT PLEASANT, not at all.
4) Drinking a 1/2 gallon+ of cleansing solution IS nasty, I watched it - but it's only one-off at least! :-)
5) Despite what some (even surgeons) may say YOU WILL NEED TO DILATE to stay open!
Depth and lubrication - though often too much rather then too little - is the plus side, with 6" no issue or even more depth (depending on pelvic build I'd assume)
6) 5 month post op with out dilating in the two cases I know, have reduced entry to less then allowing little finger to pass!! I actually seem it (gynaecological).
7) I myself had inversion with the 'standard' scrotal skin graft (3rd op in 1 week at PIH) and now have a little under 5" depth, depending how one measures AND the positioning one's pelvis.

If your partner is long > 5 ½", and never mind big in girth, it then may be the way to go...
9) Our local surgeons proclaim it is either inversion - or colon-section, this to my knowing from PIH is NOT true.
Dr. Sanguan does secondary colon-section if inversion lost too much depth over time, say is down to 3 1/2" and intercourse becomes difficult, painful or what ever.
My two cents, and YMMV
Axelle