Accordion bottles are potentially the worst possible choice for storage.
They are just about impossible to thoroughly clean, and their pleats are prone to letting oxygen through.
A glass bottle with a good cap is much better.
If you are concerned about handling glass, a heavy walled PET bottle with a good cap is very good - think of the material in good quality soda bottles.
I fully echo Matt's statement. The price of MG developer if bought by the litre is comparatively expensive. so I buy mine in 5 litre containers which, when I open the contents are decanted into 500cc brown glass screw top bottled. The (non child lock capped type) but with polypropylene seals. In the smaller containers with an even smaller surface area exposed to air the 2 years stated by Ilford may very well be pessimistic.
I can but the 5 litre containers for around £39 but 1 litre containers from the same source are around £12 per litre so a saving of almost 20% The glass bottles are bought from a commercial supplier for about 50p each, but they are reusable so you only buy them once.
Before use I further decant a full 500cc bottle into 5 x 100cc. I find that unless I am making a number of 12x16 prints. 100cc of developer is enough for an evenings darkroom printing. If you only make 3-4 10x12 prints then the diluted developer will probably be safe to use the following morning.
The inventor of concertina bottles should be indicted for crimes against photography!