Think of a plumbing system. The FNO provides the "pipes" - if those are problematic, you get blockages (congestion) or leaks (last mile packet loss and session drops) and sometimes even breaks (outages). This said, the way the pipes are designed and upstream pipes used (backhaul) can influence the quality, throughput and reliability of a connection. L2 (the plumbing) is deceivingly tricky at times - same as in a house's plumbing, the selection of kit and the way it's set up dramatically affects the pressure and reliability of the water that is to come, and just because water comes out the tap, doesn't mean it's the best way to do it, nor is that water flowing the way it really should.
The ISP on the other hand is the water in the pipes. ISPs can control where it comes from (latency to various destinations), how much is available (contentions, throttling and speeds), what flavour to add (special work on the packets and for ISPs that do, shaping the availability of certain protocols). Each ISP usually has its own unique flavour of water in the pipes. ISPs can also drop sessions (if their kit is under duress) or have constraints of their own on their networks.
Essentially, you want to be on a FNO (if you have a choice) with a track record of providing a decent L2 service to ISPs (well designed networks, quick maintenance and support and generally quick response to L2 issues). And with ISPs, well you have many more choices and should consider factors such as support (seeing as they usually interface between you and the FNO), network (latency and general capabilities), reliability etc.
) that the move from an asymmetrical 50/5 Mbps to a symmetrical 50/50 Mbps is as much as I can expect from the Vumatel price changes.
