Hey Darthpasquin, Welcome to the Forums.
I'll try to help out a little as I had many the same Questions when i was first looking to get a sabre, and recently got a Diamond one myself.
Basically there are two broad types of sabers stunt sabers with no Sound at all then sabers with Sound.
With Sabres with Sounds there are different Types
Saber with Basic Sound - has basic sound just like the name and uses 4AAA batteries, you choose only one colour for your sabre and perhaps a flash on clash - what that means is when your sabre hits something it flashes a different colour for a brief second or so e.g. a Gaurdian blue with Silver flash on clash is Blue 90% of the time but then when the sabre impacts something hard enough will flash white. the Sound on these sabres is fixed to the regular Obsidian sound board - this is a generic kind of lightsabre sound suite - there is a special sound when you switch it on (the snap-hiss, sounds for different swings, spinning, stabbing and clashing.
One thing to be clear on is all sabres with sound will automatically make sounds when you move and swing them etc. That was a concern and question i had as well and am happy to say they are built with motion sensors to make sounds as you swing no need to worry about having to program something yourself.
Although it is called 'basic sound personally i love this standard sound set it is a classic lightsabre sound.
Sabres with Premium Sound (of which i own one) - are the next step up, the main difference to a sabre with light sound is - it is powered by different batteries rechargeable Li-on specifically but that is cool you get a charger with it when you order so you will have everything you need to recharge them, and the premiums sound v4 comes with additional sound fonts - that is different suites of sound to use in addition to the standard Obsidian sound e.g. Blackstar which has a more 'dark' sound, Ancient sabre with is more crackly. You change sounds fonts by holding the button on for a few seconds so can always change back to original.
With premium sound you get one colour choice and can choose flash on clash as well as explained above.
Not fully up on Emerald but do have a diamond.
Diamond sabres - contain 4 lights, one of each standard colour - Red - Green -Blue - White - if your order say a regular Red sabre you just get one Light in it the Red, here you get all four together so no difference in brightness - The Diamond controller lets you combine these colours to make almost any colour imaginable - you hook up your sabre to your computer and use free software to program it BUT it comes pre-programmed with 8 different colours! so you already get straight out of he box a sabre that can turn green, blue, yellow, orange, red, aqua, violet and yor choice of colour when you order - each with a different sound option as per premium sound. so Diamond is the ultimate in customizing if you want a sabre that can be any colour at all. Overall you can make up to 16 different colours on your sabre and change them on the fly -ie you just hold down the button make a gesture and you switch colour (don't worry you can't accidentally swap colors you have to perform certain gesture).
Hopefully this helps out a bit and is not too technical - there are a lot of options so i get where you are coming from.
But for a cosplay and just display and fun as you indicate if you are just after one color you don't need diamond. If you are happy with just a really cool standard sabre sound then Light or Premium is great - i would recommend premium obsidian v4 because you get rechargeable batteries and the sound options - even if you find you still prefer the standard sound as I do, its only an extra few dollars and you get the option there if you want it. Diamond is not 'better' so much as just different and give you more options, what is best is what suits your needs.
For a coupler I would say a flush coupler would be best the same colour as the sabre you intend to get, e.g silver flush coupler if you go for two silver Menace - but I'm sure others can help you more with their experiences on that topic, lining up buttons (I don't own a Menace myself) and Emerald details.
No doubt the other guys will soon help you out too with their advice - I would also recommend checking out some review videos on the forum and youtube so you can see emerald, diamond and standard sabres in action hear the sounds and see the colours. The Ultrasabers youtube page also has some videos explaingin what the diamond and emerald controllers are all about in more detail.
And you can always contact customer service, the have always been great to me.
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