So my first experience narrating for my group with an summoner in the party.
Let's start with what the group is:
Barbarian weapon improviser, ranger flurry using fans and the assassin archetype, edge ranger with an crossbow(Plans to go for the EA route later), sorcerer dragon arcane, eidolon dragon. All level 4.
The campaign is a homebrew thing but mostly stealing stuff from Irrisen and the Land of Linnorm kings. The party start at a bar, the people there have a few problems as the members are unusual races(2 kenku, 1 ratfolk, 1 shoony and a gnome) but they do manage to talk, the gnome summoner does unsummon the eidolon because most people seem well... Not particularly receptive of the dragon. They manage to talk to everyone then proceed to find a shady character inside the bar. Most skill checks went without a hitch and they avoided a fight even when the dog hid under a table and pissed on someone, they negotiated with the man and got a contract for 100 gold pieces and 1% of all the loot inside an ice cave that seem to be used by a cult before.
On the first optional puzzle(That they were supposed to just examine find an light arrow that was hidden deeper into the dungeon or have someone cast light on it... They decided to smash the reward instead and broke the loot) the fault was of the weapon improviser and the summoner almost solved the whole thing but they broke it before. The skill checks for finding traps were not hard and mostly solved by the summoner using level 1 summoning spells for the two fireball traps and the ranger flurry using perception to notice the icicles on the ceiling and then using a 10 foot pole to to trigger them.
There were two combats the first one was with 4 level 2 icicle snakes then later on 2 level 3 icicle snakes. The first one was easy for the summoner he picked an eidolon with fire breathing even with high ref saves the weakness made the summoner damage quite high. The flurry ranger had a hard time as he uses fans for his damage(He plans on a fun build using the new heavenseaker archetype not sure how it will play out) and his rolls were awful besides the fact there were no space for his backstabber to work properly, the ranger with the cross had heavy hits each time and the weapon improviser well... Improvised with high damage. The persistent damage destroyed the party taking the sorcerer to his last wits and 1 hp.
The second combat was awful for the party, the snakes were hiding in icicle form and no passed the perception check so they just ganged on the sorcerer and the summoner... The shared hp pool makes the summoner quite durable... But also is quite confusing as after he took damage he forgot that the eidolon shares the pool and then sent him to the frontlines to use the breath weapon while he retreated... That did not work well as the eidolon took damage and the summoner fainted while taking persistent damage. Luckly the precision crossbow ranger dealt a lot of damage again and the weapon improviser and the sorcerer finished them off but one escaped.
Finally the boss was an Blizzardborn in the last room, they ganged up on him and pretty good rolls made the fight quite easy. Except for when the blizzardborn started using walls to just well kick ass by slipping in and out.
My thoughs were that... Summoner seems decent, there's a few things rough around the edges (Act together 1 action limit that was discussed before with the fix seems fine.) his bonus being lower than a member by 1(Boost eidolon should probably give an circustance bonus... or maybe an status bonus) to the eidolon seems like a small fix.
The shared HP is... Weird to manage because when the hp is low your plan is to run but the eidolon wants to frontline so it's an awkward thing as you need to consider 1 pool of hp only. But that is better than two in my opnion as we can keep the eidolon in a better power level compared to separated ones.
Saves where not much of a problem almost never the summoner was close to the eidolon.
Not having access to an summon pool hinders the class a bit... The summoner had to prepare summon spells just because he wanted them when he maybe should get 1-3 a day for free that would get a lot to the class.
The spells were fine as he does not need to use them often and good cantrips do help the class in case he needs to get away from a fight with the eidolon.
All in all the class seems good, i will keep going with it to see how it goes.