The potion can only be used on yourself and only to heal.  The Universal gadget can be used to finish off an opponent, heal yourself, or heal an ally.  It's the fact that it gives you so many options that makes it less powerful than it's potion counterpart.

agreed

I'm not a big potion user, but I never pop potions as soon as the cooldown is up, it's just too expensive to play like that.  The Universal Gadget takes one slot and it is versitile.  If I'm chasing down an opponent that is low on health I can use it to finish them off or if I'm running away I can use it to heal myself or I can use it to heal an ally that is in trouble.

Even assuming there was a direct damage item and a heal ally item (which there aren't that I know of) the gadget would still have it's place doing less damage and healing for less because it's a 3-in-1.  Sure, I can only use one of the 3 things but I can wait until the last minute to decide how I want to use it which is what makes it worth 500g.

Yah, program likes the Gadget.  We never got to finish that 1 v 1, btw ^^

You are paying for versatility in a small package.  Yes, you can field various other active items that are more cost-effective at any one of the Gadget's functions.  But each of them will take another item slot, and all together they will cost alot more.  The slot limit alone makes this a very good thing to have, generally, even if you are playing a support Sedna.  (Incidentally you shouldn't be healing yourself too much in this role - you sure that's how you'd describe your build?) 

Below level 10 or so the Gadget can change the course of a 1 v 1, and it leaves you room for your warpstone and your portscrolls or mana pots, etc...

Wrong. I know exactly what i am going to use it for: heal my partner.
I won't heal myself with it, i prefer my single heal, or a potion if really needed.

In fact i'm playing a support Sedna, i rarely have to heal myself, and i'm looking for items to improve my team healing potential.

I already use the area heal (favor point item), Sedna's single heal, and the gadget.

My healing combo is Single Heal (SH) => Area Heal (AH) => Gadget (G) => Single Heal (SH) => Team Speak: Hey mate now you take care of yourself, all my CDs are... down

But now that i've play lot of games with this build, on balanced fights my partner have to 'waste' time and golds to use a potion. Hell, he's got a healer (healbot ? ) with him, why would he had to use a potion ?

I understand this need of multifunction item for lot of demigods, but i this particular case, i only need one function, which needs to be upgraded to make the char build really effective in his role: team heal support.

But now i wonder if the problem isn't the Gadget heal value, but the Sedna's single heal cooldown...

With a shortest cooldown, i could SH => AH => SH => G => SH

Why not G before AH ? Because of the 500 golds After the first heal it's hard to determine if you'll have to use G or not.

But it could be, still with a shortest cooldown: SH => G => SH => AH => SH => G => SH
That would be a great healing combo.

But still i'm ok with your arguments of multifunctions for lot of builds, but not this one : /

Moko.

We're still testing, but for the moment we focus on Rook, full dps build.

He has great hp pool, but in long fights he has to use potion, on late game especially.
Ennemies over dps my heals And we are not in a MMORPG, so there isn't stuff with +healing spell

hmmm.  I remember Rook had a decent dps build in previous Betas, but I haven't seen it lately.  Rook putting all his points in Stats and God Strength?  Attack speed, wyrmskin, and crit items?  

Or you talking about Boulder and Hammerslam? 

Rook is a great tank when Sedna supports, but you still need some nukes if you want the battle to end favorably, imo.  Pounce + Hammerslam is really strong.