Is it time to get your feet wet?
I'm not sure that I am the best one to talk about siphons. I've used them. I've made some bell siphons but never been as good with them. I've had many many loop siphons and they usually work quite well providing conditions are right. I have also built FLOUT's and they are great if the situation warrants.
So what would make some one mess with siphons? Isn't it easier to just run the pump on a timer and let all the beds flood and drain at the same time?
Well, in my original set up, I ran siphons on the beds and my pump ran continuously. The reason to run that pump continuous was based on the type of pump as well as the way it was installed (inline non self priming pump above the water line of an in-ground tank.) So, I ran siphons on the beds so I could run the pump all the time. The constant filtration was good for the fish and bacteria but I think some of the plants might have been happier with more dry time (mainly the ones right by the water inlets to the beds.) When running siphons, it is important to make sure the drainage through the gravel is good (better to go with larger gravel) and that the gravel guard around the drain lets the water flow freely enough that it doesn't affect the siphon operation too much.
Siphons require a flow rate into the bed that is within a fairly specific range for the siphon to operate properly. If the flow rate into a bed is too slow, the siphon may not start properly and the water will only trickle out at the same rate as it flows into a bed and a equilibrium of constant flood is maintained. If the flow rate is too fast the siphon may start but not be able to stop properly and an equilibrium of constantly drained may be the result.
Sometimes people make adjustments to change the way a siphon behaves. Like adding a trap at the bottom to make it harder for the siphon to trickle over before it starts, this can sometimes get a siphon to start even with a slower inflow rate but it also can cause issues with the bells on bell siphons floating or it can make it harder for the siphon to stop properly since it causes the siphon to have more trouble getting a good gulp of air to stop it properly. This is why many siphons that have a trap on the drain will also require a breather tube into the top of the siphon in order to allow it to break when the water level is low enough.
I don't have much experience with the Affnan siphon design but I have gathered that it works very well provided there is no air trap. The Affnan siphon must drain freely in order to take advantage of it's benefits. This might not be possible in some drain configurations where there isn't enough fall to allow for a free drain with no trap.
Another device that I have tried was a FLOUT. Stands for floating outlet, it is basically a box on the end of flexible tubing that is attached to the drain. The box floats up on the water but when it reaches the end of it's range the water rises till it can enter some holes on the box at which point the box floods and sinks allowing the water to rush through it and out the drain. If you have the space to install one, they are great!!!! So long as the inflow is not faster than the drain pipe can handle, a FLOUT can deal with any inflow rate that is less than the drain rate. A FLOUT could replace the flush valve in a barrel flush tank. A FLOUT can deal with a mere trickle of an inflow, it doesn't care. The only real drawback I see with a flout is it needs a space in which to move freely as the water rises and falls, this can take a fair bit of space from a grow bed or it can be installed in a separate bin but that still needs space level with the grow beds that are being served by it.
Are siphons worth it? Well that will all depend on the situation. I still use them in a few locations. I have a half barrel that uses a loop siphon and one of my rubbermaid grow beds that gets a constant inflow is being flooded/drained by the use of an external gooseneck siphon (basically a loop siphon made with hard PVC.) I have two other (currently constant flood) grow beds that I may try to arrange some sort of siphon or FLOUT arrangement for.
Does this answer may questions? Or just bring up more. I'm sure I will need to provide some links for more information. Perhaps Affnan will pop in with a link to his siphon explanation. I've never really worked out the math on specific siphons and flow rates and how best to build bell siphons and now that I have Aquaponic Indexing valves, I don't have nearly so much need for many siphons.