Mantas

I have a 12v BlueNova “drop in” on my electric fence energizer. It’s been running for 2.5yrs no problems. 
 
I have a 24v Red Pole LifePO4 drop in on my garage door motor. Been about 6 months. No problems. 
 
I have a 12v el cheapo lifepo4 on my Centurion gate slider motor. Been about a year. No problems. 
 
I have another of the 12v el cheapo lifepo4 dropped into my house alarm. About 2 years now. No problems. 
 
All of these were direct swaps with the old LA/Gel batteries. No changes to charges etc. 

I have 2 sets of drop inn's and yes I have 2 x S-100 and they have never switched off. Wonderful battery. Just like other batteries in series just use a balancer to balance between the 2 or more. The BMS in each one cannot cater for it. 
It is not enough to ensure the 2xseries is at the correct series voltage as one might be lower than the other one while the series voltage is correct. 
I use the HA01/02 balancer. 
This is just like 1 guy has a x inverter and rate it scrap while the next guy has the same and is happy with it. 🤔🤔

There is also the issue of keeping the batteries balanced, most cheap inverters just charge both in series. Check the maximum charge
voltage does not exceed 28.4v at the tail end of the charge cycle. A bad BMS can wreck a battery. I would rather fit a single 24v lipo with the right protection.

Without looking at the video (sorry, time is tight), MEN (Multiple Earthed Neutral) seems to be a type of TN-C-S where there is a neutral to earth bond at the DB. That's what we have in Australia, and multiple bonding is a no-no. So (if I'm right about MEN being a type of TN-C-S), the above statement isn't true for all TN-C-S.
For that subset of TN-C-S where there is no bonding at the DB, then it seems to me that putting a permanent bond at the inverter output would be harmless, though it may be annoying in some way for the network, and may be illegal. I don't know anything about South Africa's regulations.
My notes also say that much of South Africa is TN-S, where there is a bond at the transformer and separate PE and N conductors. In that situation, without thinking about to too hard, it's possibly dangerous to bond neutral to earth anywhere, as you might end up carrying a tiny fraction of neutral current, which could overload your local system. I think in that situation you have to bond the inverter neutral to Eskom's neutral, and trust that connection all the way back to the transformer. But TN-S is based on that trust all the time, it seems to me.
In summary, I don't know enough about the SA situation to be useful; I'm just raising more questions. Sorry.
It seems that this subject would be good to sort out once and for all and publish on a forum like this one. Presumably, (most of) the electrician installers are aware of the situation, but there seem to be enough DIYers who just want to add an inverter for a granny flat or shed etc. and don't want to spend a whole lot on it, and it would be good to know how to do it safely.