These are my own observations rather than a technical review. I've not really have had much chance to stretch the legs of the units yet.
I recently purchased a pair of 400BX and a 300RX unit for a small studio set up. I also got a beauty dish and a 135cm Octabox (see my previous thread for the full list).
Design.
I much prefer the matt grey of the 400BX than the semi-transparent casing of the RX units. This said both have clear and well laid out buttons on the back that give a positive feedback when pressing. Both sets of lights are compact and easy to carry. The Elinchrom ring system takes a bit of getting used to and can be a pain when trying to attach large modifiers. However having a handle at the back of the light also makes it easier to move and/or tilt the light back to make adjustments and fit cables plus it gives a readily available carry handle.
Power.
The 300 unit has more flexibility than the 400s because of the stop range. This would be of great use in smaller studios and/or situations where you want more control over the light.
This said the 400 has a pretty decent and useful range when in a normal studio environ but for the extra money you will have to consider carefully which will be more useful.
Triggering.
Throughout the shoots I used the 300RX on a boom with either a grid spot or a beauty dish. I triggered the 400BX with it’s light cell. Both performed flawlessly and the remote control over the 300RX was a major time saver especially when it was mounted on a boom. The Skyport Transmitter will only control the power with +/- increments and doesn’t give any feed back to actual power. For this you’ll probably need the USB transmitter and software.
When using the 400BX on it’s own with a Skyport universal it didn’t miss a beat either.
Overall I’m impressed with both units but if you have the cash I’d get the 300RX over the 400BX for the extra control over the output and more importantly the remote control features of the Skyports. It can’t be over-stated how useful this actually is when working with lights especially in hard to reach areas such as booms.
This was taken with just the 135cm Octa and a 400BX.
https://photography-on-the.net/forum/showthread.php?t=503328

