In practical terms, the main issue is that the cable/busbar entries aren't standardised - while the form factor (overall shape in terms fo DIN rail fitting and opening in the front panel) is. As long as the different devices aren't pulling the busbar in different directions (typically further away or closer to the DIN rail) then there's likely to be no problems at all.
In theory, there could be electromagnetic interference between one of the RCBOs and the adjacent RCD, but personally I think that's unlikely.
What you can see, and which would be more of a concern to me, is that if you look at the main isolator, I suspect the terminals were tightened by a gorilla on steroids. The case of the switch is distorted (the printing doesn't line up across the two case halves of each pole), and it's tilted slightly to the right - so by the time you get the case front on, you end up with the gap above the other devices visible in the photo.
But, if having an EICR done, then the inspector (if they actually inspect rather than make up some test results and fill in the paperwork in the car outside) will flag this up. In a domestic situation, the regs require the use of a type tested distribution board - and since manufacturers aren't in the habit of approving mixes of their own stuff with random competitors, that means using only the devices the manufacturer specifies for that board. My guess would be that the EICR flagged up circuits "not to current standards" due to lack of RCD protection, and the previous owner had these RCBOs fitted to fix that. The EICR should show either non-RCD circuits, or the non-compliant devices.
Some will disagree, but I'd give this a C3 (improvement recommended) which leaves it up to you whether you wish to change it.
Changing the board is an option if you wish to, the fact that it's a plastic case may be cause for another C3 - but that's open to even more debate (many wouldn't even flag it, especially if it's not somewhere where the case burning would impede exit in the case of an electrical fire in the CU's innards*.
* <rant mode> Current regs (because they were very very badly written) require a ferrous (steel) case. Consensus isn't that there's a problem with plastic cases (and conductive steel ones introduce their own risks), but that the London Fire Brigade (LFB) observed an increase in fires starting at the CU and therefore demanded that "something be done". The fact that the rise in fires coincides with the rise of (so called) "smart" meter installs by people dragged off the street and pushed through the shortest training possible didn't seem to have occurred to either the LFB or the committee that added the requirement for steel boxes.
The regs don't actually specify that a steel case is required, they specify that the case be non-combustible without specifying what that means (e.g. by refferring to existing standards on material combustibility) - and thus making it effectively impossible to comply. But they added a note that ferrous metals are deemed to be non-combustible, and thus created a situation where the only route to compliance is with a metal box, even though there are plenty of other materials that could comply if the regulation specified what the criteria were.<end of rant>
