The problem is if you are a 2 day a week commuter you have a high likelyhood of not getting through your 8 days in a 4 week period.
If you are a two day a week commuter, you would be better off speaking to your employer and telling( not asking) them that you will be working flexi time with a post 10am start.
That way you will save 1/3 from peak time fares, and potentially more with applicable railcard.
You would save more doing it that way and buying individual tickets than you would with one of these flexi seasons.
lets take luton to st pancras travelcard season as an example.
weekly ticket is £221
flexi is £221
monthly is £549
8* super off peak travelcard £193.60
8* super off peak travelcard+ network railcard = £127.60
The overall value on the flexi tickets is nowhere near compelling enough.
If they had them on offer for 8 days in 28,calculated at close to off-peak price rather than peaktime, then there would be a case to answer for them.