The so-called chainsaw oils have a manufacturers name on them so they are bound to recommend their own make of oil
2 strokes run on various different ratios ie 25/1 50/1 etc It is up to the user to mix accordingly. You can buy a small bottle. and I'm sure that most of us will have seen them at some time, that you pour petrol into first, up to the 1 litre mark. You then pour in the requisite amount of oil to the various marks. The good thing about this is that if you are an occasional saw, brushcutter user or whatever, you will not have litres and litres of fuel lying around going "off" Petrol does have a habit of going "off" Most problems with small engines come from varnishes forming in fuel lines due their lack of use.
If your saw needs 50/1 there is another alternative and it is Aspen 2T.
http://www.aaoil.co.uk/environment-Aspen-2T-alkylate-petrol
The best thing about this is that it has a shelf life of 25 years. No need to add anything, just pour it in and off you go. It appears to be expensive but if you factor in buying 2 stroke oil it is quite affordable. Another plus is that the fumes from it don't appear to be as unpleasant as normal petrol & oil mixes.
Regarding using Chain oil: A lot of the more recent oils seem to have been to placate the Bunny huggers in that they are biodegradable.
I have used waste oil in a Rancher 50 for many years and it doesn't seem to have done the bar or chains much harm - and it's very affordable
These remarks are a personal opinion so please don't come to me if your chainsaw falls to bits