The comparison that basilisk gave above compares damage dealing astral construct 3 to two other creatures from the summon monster 3 list.
I purposefully chose 3 because it is around the time when they are somewhat equal but from this point on the summons really start to have such a wide variety of abilities that there isnt a way to compare them very usefully (summon monster 4 also has a celestial lion, and that guy is pretty rocking)
However, it does fail to take into account a few important things.
1) Reach (pretty nice ability here)
2) SR (all summon monsters have it)
3) Energy resistance (nearly very summon has it)
4) communication (all creatures of int 3 or higher understand at least one language, which is common unless specified otherwise, it is not as far as I can tell, so communicating with the animals shouldnt be much of a problem)
5) Scent (this one is 'huge'. this means that the creatures can get around invisibility to some extent and be able to perform other tasks as needed)
6) Skills (listen and spot are on most of the creatures somewhere, plus for the ones here the ape has a massive climb, which can be useful. Lots of options is what the summon monster list seems to try to be about, it doesnt always do a good job though).
7) Saves (astral construct saves tend to be pretty poor, the 9th level version has +6 to all saves, both of the two guys here for summon monster 3 almost have that [+6/+6/+2 and +7/+4/+1]
8) Specials (such as the hell hounds fire breath, with this guy at your side you might actually be able to kill off that troll, none of the other three guys are able to do that, or the earth elemental to walk through the ground to find out which tomb is the fake, or whatever other options may come up)
Here is the list that astral constructs get to choose from:
SRD:
Buff (Ex): The astral construct gains an extra 5 hit points.
Celerity (Ex): The astral construct’s land speed is increased by 10 feet.
Cleave (Ex): The astral construct gains the Cleave feat.
Deflection (Ex): The astral construct gains a +1 deflection bonus to Armor Class.
Fly (Ex): The astral construct has physical wings and a fly speed of 20 feet (average).
Improved Bull Rush (Ex): The astral construct gains the Improved Bull Rush feat.
Improved Slam Attack (Ex): The astral construct gains the Improved Natural Attack feat.
Mobility (Ex): The astral construct gains the Mobility feat.
Power Attack (Ex): The astral construct gains the Power Attack feat.
Resistance (Ex): Choose one of the following energy types: fire, cold, acid, electricity, or sonic. The astral construct gains resistance 5 against that energy type.
Swim (Ex): The astral construct is streamlined and shark like, and gains a swim speed of 30 feet.
Trip (Ex): If the astral construct hits with a slam attack, it can attempt to trip the opponent as a free action without making a touch attack or provoking attacks of opportunity. If the attempt fails, the opponent cannot react to trip the astral construct.
For flying the hippogriff moves at 100 whereas the construct moves at 20. The hippogriff may be ridden but the same may not be said for the construct (I would allow it with a sufficient craft(sculpture) check but with penalties to the ride check). The hippogriff again has 3 attacks, low light vision and darkvision, scent, and saves that beat the astral construct there and back again.
Construct type is pretty nice, for this case basically granting: immunity to mind effecting, Immunity to poison, sleep effects, paralysis, stunning, disease , death effects, and necromancy effects. Not subject to critical hits, nonlethal damage, ability damage, ability drain, fatigue, exhaustion, or energy drain. Immunity to any effect that requires a Fortitude save (unless the effect also works on objects, or is harmless).
Of course there are spells that specifically do more against constructs, but those arent terribly important here.
The magic circles work, assuming that the proper alignment is choosen and the SR is bypassed (likely to be, but there is always a chance). Of course those usually only work less than a third of the time to begin with and the SR might kill it (so I will lump it in the same area as the spells that hurt constructs more).
Again though, I picked beatsticks to compare with because if the summons could beat them (and even in the cases given here they tend to win at least half of the time) and since the summonings have so many more 'specials' that they tend to get in abundance then the winner is pretty clear.
Effectively the astral construct is only a beat stick, although it does tend to be pretty good at it. The higher up one gets on the summoning not only are more beat sticks gained (some of which are incredible) but also the number of other options (such as spells, special abilities, whatever) opens up dramatically as well.
I like astral construct a lot, I think it works perfectly for what it is meant to do. However, in no way to I think that it is worth anywhere near 9 spells. Pretty much worth 1 seems about right.
The greater variety of options, getting multiple abilities at the same time (more than just a single menu choice, although later on the constructs do start to get a couple of things they were missing), and the spell like things that one can get tend to even the two out over the course of the levels.
(if we go to the end case, level 9, we have the elder elementals, or the gargantuan fiendish monstrous scorpian, or a few other beat sticks, anyone want to compare those?

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