Handheld AA really isn't that hard to use once you know how and once you understand how it truly works you can use it to your own advantage.
For starters let me explain how seeking works in BF2. To start with there are two types of signature, heat and laser. Heat is used by every air vehicle and the flares and its what AA missiles lock onto and what makes the boxes on the HUD of an AA weapon. Laser signatures are what the SOFLAM uses, and in vBF2 are attached to the vehicles themselves like the heat signatures are attached to aircraft, but in vBF2 only air to ground missiles from fighter-bombers can lock onto them. Now while different weapons lock onto the different signatures, how either weapon behaves with these signatures is pretty much the same.
Basically you have two stages of weapon locking, which is first HUD locking, then after firing, weapon locking. This may seem strange but the HUD locking dose nothing more than fire the correct weapon state, it dose not control where the missile will go or what target it will lock onto once fired. The reason why HUD locking needs to be done is firing a weapon without a HUD lock, your basically firing an un-armed weapon which has no tracking what so ever and will just fly strait, or off in a random direction or w/e depending on the deviation code and other factors (in the future we may even make the missile not explode if launched without a lock due to a common exploit with firing the weapon non-locked currently). Also the HUD locking process can tell the difference between friendly and enemy vehicles, with a big "X" over friendly targets and not letting you lock onto them., reason for telling you this will come apparent later.
Once you have a HUD lock and then fired the weapon, you fire a weapon that will track the closest signature of the type it locks onto (heat or laser). Now the closest signature might not actually be the one you locked onto on the HUD. Most of the time it will be but some times there might be a flare or some other signature that is closest to the target in the "Locking Field of View", aka "Locking Cone", aka "Locking Angle". If this is the case, the missile will go for that target and not the one you want it to go for. What might surprise you is once the missile has been fired, it has no idea what team the missile belongs to and will go for ANY target, friendly or foe. A good example I'm sure many of you have seen is in vBF2, you have a J-10 chasing a F-35B, and you fire at the J-10 and the missile misses the J-10, what dose the missile do next? Yep that's right, it goes after your friendly F-35B and kills it... Now while that scenario isn't common in PR due to our missiles having a much larger detonation radius, so a missile is unlikely to miss an aircraft like that by a fraction like it can in vBF2 and then go after the next closet target in its FOV once passing its original target. How ever this factor still applies to many things in PR. For example if you have two choppers in the sky, one friend one foe, the friendly is closest to you but you lock onto the enemy which is slightly further away, you shoot and the missile once fire, will slam into the friendly chopper. One area you can exploit this factor to your own advantage is with the flare system, where you can fire at a flare, and depending of the angle of the flare and your launch point and the aircraft you want to shoot down, you can get the missile to initially lock onto the flare, miss the flare as it wont explode on the flare, then go after the aircraft you want to shoot down. This takes a lot of skill to do but if done right, it gives the pilot so little warning that there is nothing he can do about it, since the missile is so close, at top speed and even if he pops flares and the missile locks onto them, the flares are so close to him that the missile has an even bigger target to lock onto although might make the missile explode slightly off to the side, but still causing significant damage but chances are, the pilot will not be able to react in time if you do that. What mainly determine if you can pull this off or not is if the missile can turn onto its new target in time which with the speed of the missiles is not something easy to do in PR.
As for "missile locking after launch", tbh I think that is people just confusing the missile being able to lock onto a new target after missing the first, like with the flares. You need to lock onto a target before you can fire, otherwise your just firing a missile which can not lock, period.
Now how you can use this to your advantage is knowing about the locking cone and other things, you can angle your initial fire from the HUD lock away from the target, possibly slightly leading it and or, away from other signatures in order for your missile to track the right target. For example if you have that situation I pointed out before, where you have two choppers in the sky, friendly and enemy, with the friendly one above you but closer to you but still in your locking cone, what you can do to somewhat help avoid your missile going after your friendly chopper is aim downwards, away from your friendly chopper but still keeping the enemy one in your HUD locking cone (ie, the HUD of the weapon is still trying to lock onto it), once locked, fire, your missile will first be heading down, away from the target but then will turn up to hit it and with any luck not seeing the friendly chopper.
Anyways hope that helps some of you, the rest of the Dev team hate my AA skillz
I was one of those guys who constantly fired the SA7 from the hip.