I've been using the income method (marriage) for 9 years now and I've never any serious issues, certainly nothing that has caused me any angst.
We were only required to have a house visit on the 1st year and we back then we needed a witness, but from then on it's been more or less routine.
The 1st year following the loss of the embassy letters was a bit nerve racking, but I'm used to the routine now. In fact this year I was complemented on my 'well presented' paperwork package. Rare to get praise from an IO! (although she did say it in Thai, to my wife!)
As @DrJack54 said earlier, 'most issues for folk complaining about extensions based on marriage is down to things such as errors in docs supplied etc'.