The differences are in the options. High level
summon monster spells give you a ton of defensive powers (SR, DR, ect.) and generally useful spell-like's. (ex: summon monster 3 can summon a dretch, who can then cast stinking cloud, which is a 3rd level spell, just with a worse save.)
these elementals seem to be more in line of the
summon nature's ally spells, meaning that they are more potent melee combatants, but have less versatility.
EX: You can summon a creature to cast wall of ice, even if you can't cast evocation spells.
I think these are a good medium, they are restrictive (more then summon monster) in both list of options and spell-likes, and they are less defensive, But they are more versatile then the summon natures ally, and much cooler from a themed caster perspective.
I think they are slightly weaker then the other summon lines on the whole, but for flavored casters (fire, ice ect) they could be effective. I would add more decent spell-likes that are flavorful. the wall spells would be excellent additions, gust of wind.
I also would love to see a shadow elemental list

. We already have spells that form shadow-stuff into real stuff, where is our shadow construct?
Side note: I feel these should be evocation spells in general, since they are molding energy sources to create a short term elemental, rather then conjuring full creatures or creating something from nothing.