Well, In reality I have affiliation with all of them, and other electronic selling websites as well. I'm a web developer. However, i'm not currently employed by any of them, I work for a MultiPhysics and Finite Element Analysis software company. None the less, i'm not here to push product, i'm here to see if I can provide quality information.
When I ordered from AccessorySwamp.com, I received exactly what is shown in the photo. I've bought the ebay cheapos too... all i have to say, is you get what you pay for. I ordered the 3500MAH from eBay here:
NEW 2x 3500MAH Extended Battery +Charger for HTC EVO 3D | eBay
I get the package 4 weeks later and the batteries look pretty close to the photo... The ebay listing says that they are 3500MAH, and on the actual batteries are labeled 3600MAH. They are the same width and height as the Accessory Swamp battery, however they arent as thick, see image below.
Also, I weighed the eBay battery and it weighed 2.0oz, then I proceeded to weigh the AccessorySwamp battery, and it weighs 2.5oz, so i'm assuming the extra weight, and the extra thickness, means more battery. I spoke with a friend of mine who lives in Shenzhen, he told me that the eBay batteries for the 3D are actually in the ball park of a 2700MAH battery.
Here are some photos I took this morning at work.
Here is a photo of the HTC Evo 3D with the OEM Backdoor, and then another HTC Evo 3D with the 3500mah Accessory Swamp backdoor.
As you'll see, the OEM and the Accessory Swamp back door is almost the same, here are some differences: The AccessorySwamp back door does not have the Red Ring around the 3D Camera, the Headphone jack does not have a metal ring, the HTC logo was replaced with a "3D", the holes for the speaker around the camera are larger, the volume and power button is a bit more flush than the OEM Backdoor. Also, the texture on the Accessory Swamp backdoor is a bit more defined and the grooves are deeper than the OEM. Overall, it's a backdoor that looks, and feels, like quality and there was some thought and reverse engineering behind it.
Here is a photo of the Seidio 3500MAH Evo 4G Battery and the AccessorySwamp 3500MAH HTC Evo 3D Battery
The Seidio Evo 4G battery was awesome, I bought it a long time ago when I purchased my Evo 4G. My Evo 4G, with the 3500MAH Seidio, didn't get much increased battery out of the box, but after I rooted it, added SetCPU, and cycled the battery, it doubled my battery life. I was able to use my Seidio Evo 4G battery for at least a solid day of decent use, no problem.
Coming from the Evo 4G, the battery performance on the Evo 3D out of the box is 2x better, and is 3x better with battery save mode. I've yet to root my 3D, that's my project for this week. However, battery life with the Accessory Swamp 3500MAH is already increased dramatically. My Evo 3D used to last me 7-8 hours, listening to pod casts, watching netflix, checking email and text messaging, on the regular... After running the AccessorySwamp 3500MAH battery through 3-4 cycles, i can use the AccessorySwamp 3500MAH all day with the same usage and it will last me an easy day, day and a half. I've yet to root the phone, i'm sure once it's rooted, battery life will be even better, stay tuned for that, I plan to root this week. i'm hoping it will last me 3 days.
The OEM back plate and battery weight 1.5oz, and the AccessorySwamp 3500MAH back plate and battery weigh 2.9oz, so it adds a little bit of weight, but it's not to noticeable when you're holding it in your hand weight wise. When you have the 3500MAH in your hand, the "butt" off the battery is larger, and make's it easier to hold, and a bit more of a handfull.
What other information would be useful? I plan to add more info when I root.
Let me know what you guys think?