Hey guys I'm just wondering why Crystalline flask would or wouldn't be a good start for a mid laner.

For example starting Crystalline Flask + Faerie Charm + 2 HP pots on Kassadin.
This means you can build and early Chalice > Holy Grail which will help later on with rift stacking etc, and you won't be too susceptible to ganks, as Kassadin, being melee mid will most likely be last hitting under tower anyway... I've done this in most of my games where I go mid and find it works really well. It helps will sustain and allows you to spam Q more at lvl 1.

Thoughts, suggestions?
Thanks!

It's fine. I like doing that on Ryze as well, in matchups where I don't absolutely need the extra MS from Boots.

For champions who won't use the Faerie Charm to build into anything, it's harder to justify. But you can substitute wards for it and it's still a fine starting item set.

It's 300 health, 120 mana for 225 gold. After your first back it probably isn't necessary, but even if it is it's 600 health, and 240 mana.

Before your first back that comes out to be: 70g worth of health pots, and ~35g in mana potions. totaling in ~110g worth of healing. Including your first back: 220g worth. If you didn't back, you could have just bought 4 health pots, and 2 mana pots giving you 600 hp, and 200 mana at a cheaper rate.

Sustain isn't bad, but I don't think the flask is ever worth it, personally.

I start Flask + 2 wards + Pots in mid lane. Gives incredible sustain. (If I'm playing a manahungry champ I buy half-and-half of HP and MP pots).
On my first back I tend to grab boots and a Tome, more if possible. (boots + wand?)

A champion that uses mana, assuming you sell the flask, pays it back after 4 uses. Without mana, 6 uses.

Yea that's what I've thought. That after your 1st back you've already payed it off, and it can be useful all the way up to your 5th back (end of the laning phase), so you rack up all this extra gold instead of using it on pots! You could use all that extra money on wards or items!

Wouldn't it still be better to start boots+pots mid if facing a skill-shot based champ mid so you can more easily avoid taking damage? But otherwise I think it is a good idea.

I've seen some high elo streams of good mids taking it... personally I just don't like the item and thats why I never take it... most of the time when I play mid its with Zyra or Ahri and I feel that gold is more useful elsewhere...