Based on the specifications, the triggers operates on 433MHz radio frequency. There are 4 channels, and works for shutter speeds up to 1/250s. The transmitter uses the 23A 12V battery, and the receiver a pair of AAA batteries.
Apparently, there are different versions of the PT-04 in terms of outward design, and I chose this version for the following reasons:
1. It is small.
2. The receiver is thin and a flash can mount on it without it being too high.
3. There is a hotshoe mount at the base of the receiver.
4. There is an umbrella holder.
One thing I like about this trigger is that I can mount it with a flash stand and a flash on top of it and uses it easily on a table for product shoots. I can also replace the flash stand with a clamp and clamp it on a shelf or cupboard, etc.
With a built in umbrella holder, you have more options now.
All in all, I like these PT-04s, and they are also very inexpensive.