To solve the unsettled dispute of which EBB kicks the most, I bought and own every single EBB M4 you mentioned as we speak. In terms of recoil, if any, the ranking of mine is:
ERG with ULYSSES recoil control weight installed > LONEX EBB with BO DYNAMICS branding > BOLT EBB (I got 2 of the new version called HEAVY RECOIL) > stock ERG > LONEX EBB with own branding and the recoil kit is sold separately (don't buy it, You will regret it unless your standard isn't high) > Marui EBB M4
If you don't mind my post in mandarin, see the link for more pics, all are my EBBs.
http://www.arms-cool.net/forum/thread-175550-1-2.html
Here is link of the review on the ULYSSES kit, every ERG owner should try it. The felt recoil has been increased a whole lot. The recoil kicks crisp and straight right back to your shoulder, not just shaking back and forth like BOLT. BOLT, however, shakes your shoulder more in other people's eyes and it also will "bounce" your red dot the most if a reflex sight is being used.
https://www.youtube.com/watch?v=FMtvJTuC5-s
This is my newest build for ERG, I hate to see a battery box on my beautiful rail, so all my ERGs are rear wired, and yes, it's so hard to find one now probably because I bought all of them last few months (rear wired ones). I heard there will be a huge restock in Jan.
I'm waiting for BOLT MB5 SWAT to arrive at Canada, I will keep you posted to see if it's the new king of RECOIL among EBBs.