Just a note, with the change to the way synth HPs are handled (to make it easier to heal the eidolon?) this is no longer an option. Fused link can, under the rewording, only be used when the eidolon would be reduced to 0 HPs.
Suggest to your synt that he used up his Real hit points first that Way he Can be healed like normal folks.
Not that big of a deal, really.
A synthesist that takes enough hits to lose their little magic powersuit just starts pulling off of his or her own HP, which can be healed by party members (not that they will since "healing in combat is the worst thing you can do"). The fact that this puts the Synthesist in danger of exploding when they go unconscious is no different than the barbarian, who has had this problem since 3.0 days.
Which also echoes certain sentiments upthread, the synthesist summoner is no longer a caster, it is a martial who happens to have some spells.
Also, some mention was made of enhanced damage dice. This isn't really fair to call it a synthesist problem since it also applies to any warrior-type who decides to get big and scary for the increased reach and damage dice, and there are quite a few ways to do it when you have a friend who will buff you. I believe there have been a few threads complaining about the damage die growth tables being troublesome and needing an FAQ.
Its more folks were touting the size increase as a feature in 'synthesist awesomeness.'
I still content only a lunatic (or severe eccentric) would want to be Huge constantly if they intended to live a medium sized society. If you want to go live with the giants, more power to you.
The issue with the hp is once you're taking hits on your tasty nougat (strawberry, marshmellow?) center you're in a situation where you're down to 'just' your d6 HD.
As I keep saying though, synth is a good choice, its solid. Its just I disagree that its 'super broken' when we've got [i][/i]...
yes going huge is problematic unless the GM allies a greater hat of disguise(and he shouldent). How do you get 5 huge elementals at level 13? And the summoner under the suit still have d8+(suits con) HP pr level if that is no good how do you handle, monks, magi, warpriests, cleric, inquisitor, alchemist, hunter and bard frontliners?