Lol no. (My turn for the pedantry)
Those irons you get on top of ACOGs are not useable sights in the slightest, suggesting they can be used to the same degree of effectiveness as a Docter sight isn't that far removed from comparing a top of the line Schmidt and Bender... to not actually having any sights at all.
They're that useless.
The only reason I would look at those iron sights in a positive light, is if I was buying an ACOG with the intention of adding my own micro red dot of some description, either a Docter or an RMR, and I wanted to buy a sight with the mounting lugs to put the red dot bracket onto. Since generally, those irons can be removed.
But yeah, they never line up properly, and the sight radius is so short that even if they were lined up right, they'd still be useless anyway. They're also not adjustable.
Additionally, airsoft Spectres don't really have any eye relief differences over ACOGs, at least in terms of clone airsoft versions. But I would imagine the 1-4x variable zoom version would have much better eye relief with the 1x zoom setting, otherwise it just seems fairly useless - the biggest advantage of dot sights is that they don't have eye relief, so if you still had to get your head within an inch or two to use the 1x zoom feature... Well, what's the point?
Personally I'd still rather have the fixed 4x version with a Docter on top of it though, I've heard that the variable zoom versions aren't all that great, and I think that I would personally find flipping between the two settings on the variable version a bit of a pain, it'd be far easier to just switch to a different optic on top of the Spectre, since then you wouldn't have to take any hands off the gun.
Though I have no personal experience to back that up with, it might work great and what I've read about the variable zoom versions being worse might just be people being overly picky or something.
Your cheapest option (if you definitely want a zoom optic) would be to buy a standalone ACOG, without any kind of back up sights, illumination or any other funky stuff with it, perhaps with a fake non-functional fibre optic strip, (or indeed just buy the one Lozart linked, though that's moronically expensive for what it is) - which you can get for around the £60 mark - then you can use the zoom of the ACOG for longer range targeting, or if you can't see your shots. Then for all other circumstances, just look down the side of your barrel and walk shots on target.
Actually, if you just want the functionality of a scope and you don't really care what it looks like, you could get a sniper style air rifle scope for even less than that, which will probably have anything up to 9 or 10x variable zoom. They just don't look as funky as clone optics.