Right time for a edit: Finally had time to watch some comparison videos. So here goes; Externally you can consider both rifles very similar, the only differences are in what style you like, whether it be a fluted barrel or not, threaded barrel yada yada it's virtually the same. Internally they appear to be somewhat different. Javelin M28 (M24) - They appear similar in size to APS2 mags, but are different in their design and do not fit the Echo-1 M28. Unknown if they fit a Maruzen APS2 - The feed nozzle is much closer in design to APS2 than the Echo-1 - Unknown trigger system, possibly APS2 but will require further review, the shells are non-standard to APS2 and VSR-10 - The hopup appears similar to the APS2 hopup design, but is not physically the same size or proportions as a standard APS2
Echo-1 M28 (M24) - At first look appear to be similar to Maruzen APS2 mags, spacing and design is similar - The feed nozzles on the Echo 1 are not like Maruzen APS2 but appear to be VSR-10 style - The trigger system appears to be VSR-10 but like the Javelin is non-standard shells - The hopup is unlike a VSR-10, although a standard VSR-10 hopup might fit - piston is not standard VSR-10 and requires special fitting to work (unknown at this time what that is exactly)
In short, until more reviews come out it's hard to tell exactly where each rifle stands. However, it's safe to say that the Echo-1 is a modified VSR-10. Because of this the internals are fundamentally different than your run of the mill VSR-10 and will require a good bit of work to get parts to fit, and that's if you can get them to. The hopup is 50/50 chance of upgradability (most likely not given the ghetto rigging usually done to make things work). The Javelin appears closer to APS2, but again the hopups are different and will most likely not fit aftermarket upgrades. ASGI has not released information outlining the upgradability of the Javelin M28.
I bought the MB06 from Well, which is basically the M28.
Here's a few things I can tell you. It's more of an SR2 clone than anything. The cylinder is not VSR, it's APS-SR2 I think (Definitely isn't like my old TSD M700). The trigger is specific to the gun. It has the L96/APS2 style hopup. You can get the PDI hopup kit for it, it will fit. The mags are gun-specific.
I will say that it shoots great. I was impressed. I can hit a 36x24" target at 210 feet about 75% of the time offhand, stock with a few homebrew mods.
The only thing I don't like is that the bolt manipulation is all of like 15º I have nothing else to say. It just feels weird. I can't tell because I've been spoiled with 4.5oz triggers for a few months, but it seems like it has a heavy trigger, which I believe is due to the 90º piston (I will double check, but I am 99 sure it was a 90º trig). The collar in the hopup also broke on me for no good reason, and the chamber is hard to get off the barrel. Complete and total PITA to try and line up the barrel just right in the hopup chamber when sliding it through the outer barrel too now that the collar's broke.