Basically, the FLR(FP) is a special case visa in order to allow a family to stay together in the UK when they can't meet the requirements for FLR(M). It's not something you should be intending to apply for - it's more an exceptional circumstances visa, issued in the case that for some unexpected reason you can no longer meet the financial requirement, which you were previously expecting to be able to meet.
It has essentially replaced the Discretionary Leave visa which in the past was granted to people who applied outside the rules and were given special leave to be allowed to stay here even though they didn't technically qualify for a visa.
If at all possible, you do not want to have to apply for FLR(FP) - it should be an absolute last resort to try to keep your family together if there is absolutely no way you think you will be able to meet the financial requirement at any time in the future, or you cannot qualify for any other visa to stay in the UK.
The FLR(FP) rules do say that the 10-year path can be applied for directly if you are in the UK, so I think you may be able to switch from Tier 4, but I believe the general idea of it is that you will have already qualified for a fiance, spousal or FLR(M) visa before and have met the financial requirements before, but due to unforeseen circumstances when it comes to renewing your visa, you find yourselves in a position where you can no longer meet the requirements (i.e. you've suddenly lost your jobs and can no longer meet the salary requirement).
The 10-year route is not ideal because it means four further visas (instead of 3) - 3 FLR(FP) visas and then ILR - and 10 years to ILR and citizenship instead of 5 years.
If at all possible, if you don't meet the requirement by the time your Tier 4 visa is up, I would advise trying one of the following over FLR(FP):
- Go back to the US in Jan 2016 and stay there until you can meet the financial requirement, then apply for a spousal visa to return. It would probably end up being cheaper and easier in the end, and would be much quicker for ILR and citizenship. Of course, it will depend on your financial situation and whether your spouse will ever be able to meet the requirement on his own if you left the UK at the end of your visa.
- Try to get a Tier 2 work visa after your studies and stay in the UK that way, then you can switch to FLR(M) once you are earning enough to meet the financial requirements. If you will have a degree from a UK university, you will be exempt from the resident labour market test and so it would be easier for you to get sponsorship for a work visa than if you were applying from the US without a UK degree.
I would suggest that both of these options would be preferable over the 10-year route, if at all possible.