Ok, I know this one might be a bit controversial but it's just based on my own experiences and my own reading. Feel free to argue with it because maybe there's something, or many things, I'm missing.
I'm pretty sure I would be correct to say that opinion openers are by far the most popular type of opener in the community, especially amongst people just starting out. This probably results from them taking such predominance in the early Mystery Method teachings.
But of the various types of opener out there (functional, screening, situational, direct etc) to me it seems, without doubt, the most flawed and least universally applicable.
The opinion opener's strenght lies mainly in its ability to "come in under the radar" and move quickly towards more relaxed conversation (A2 for those of you most familiar with the M3 model) without too much thought going into a transition phase. But here's where I feel it's over-rated. With a little practice it's actually quite easy to deliver a congruent transition from a functional or situational opener. Whereas the more ballsy openers such as direct or screening, though involving higher risk, don't need a real transition phase at all and in some cases can even skip straight to qualification.
With that in mind, the main 'pro' of the opinion opener is largely negated with just a little extra work or a little extra risk (that extra risk isn't even such a big deal if you have strong inner game... and of course if you don't yet have particularly strong inner game, which comes largely from positive results over time, you can simply use one of the less risky opener-types with a transition).
So the question, now, is "does the small amount of extra work required for other opener-types outweigh the negative aspects of the opinion opener"? And, as I'm sure you guessed, I say yes!
So what are the negative aspects of the opinion opener? Well for me the main one is the lenght and complexity of most of them. There are really very few situations where, I feel, you can walk up to a complete stranger and hold their attention for a full-lenght opinion opener. Lets say you're in a loud bar or club, in order to deliver an opinion opener fully you have to practically shout in the persons ear. It's practically impossible to then move into normal conversation in such an environment. Considering that, in a bar or a club, most girls are out to pull anyway and already have reasonably high buying temperature, it's probably much better to use a screening or direct opener. Lets take a day-game approach, the girl is busy, possibly on her way to something important. It's very hard to add value to a girl by stopping her and delivering this long winded question regarding your life. Wouldn't it be much better to simply ask a basic functional question that, by social conditioning, she feels compelled to answer? "Excuse me, do you know somewhere around here that does good coffee"? From that, with a bit of extra work you can transition to some very short normal conversation followed by a #close. Even in places where an opinion opener might normally be used, I have personally found this type of functional opener/transition to be much more effective for building a basic level of comfort in order to begin the interaction.
Another problem with opinion openers, again related to their lenght, is the difficulty with memorising them. I personally find it very difficult to remember and delivery an entire opinion opener while still concentrating on my body language, tone of voice etc.
My third main problem would be delivering them with any kind of congruence. Lets say you're in a club and decide to open a 2-set with something resembling the Jealous Girlfriend opener. You walk across an entire room to ask this random group of girls their opinion on the matter when there were 2 not as attractive girls standing almost next to you! Kinda kills the whole "coming in under the radar" aspect. At least if you use a more direct opener you are being congruent. And what's more, you're showing confidence and some kind of an understanding of female sexuality.
I'm sure many will disagree with this but it's an important point I had to make, even if just for myself. Essentially, for night game I say go with screening and direct openers... for day game use functional and situational with a transition. This is obviously an over simplification. Direct game can work wonders during the day while situational openers can sometimes be your best bet in a bar or club. But that all comes with a sensible appraisal of the situation at hand
