Opinion on Glyph MP5?

Not worth it. Conservative play and working on the accuracy of your abilities will retain more mana than compensating by replacing your runes with mana regeneration.

If you start Doran's Ring, it also does regenerate a lot of mana. One wave of minions is 24 mana + the innate regeneration it provides.

I wouldn't bother with them; Flat/Scaling MR or Scaling CDR Glyphs are far more useful in pretty much every situation.

I find that 2 Doran's Rings and Morellonomicon (200% additional base mana regen combined) are more than enough mana regeneration for me.