The Airlink  Transformers aren't bad at all as far as off the shelf units go.  However in comparison to bespoke units  they are found lacking. But then they are made to a price so that is totally understandable, and they are no better or worse than any other mainstrea and they are no better or worse than any other mainstream manufactured transformer.  The ones that I buy are slightly more expensive but in my view the outcome was and justifies the slight increase in expenditure.  However the transformers that I have made for my balance power supplies are a slightly different design altogether. 

I would challenge the view that Airlink TX's are found lacking. I have an Airlinks BPS and it works perfectly in my system bringing an overall improvement to sound. Furthermore, mine is a bespoke 2Kv version having been wound for a more realistic 240V instead of the standard 230V spec. Generally it is totally silent in operation. The only time it buzzes is when the amp is switched on with the corresponding current draw and peculiarly for a short while between 4:30 and 4:45pm every day. This must be something switching on outside of my property as it's nothing in my home. I have also introduced a DC blocker board on the input before the Tx. Airlinks TX's can't be that bad. NVA use them for their BMU!

See my recent diagram Kevin.  Its not specific to Balanced Power or Mains regenerators.  RCD's can only detect faults on circuits physically connected to them.  There will be no physical connection on the brown and blue wires coming out of your regenerator to the brown and blue wires running through the RCD's (I know the colours are different here in France, but you know...).  A fault on the output of your power regenerator could no more trip the RCD on your consumer unit than it could mine - for the same reason - they are physically isolated.  It's testable. 

linkrcd tester  Conforama stock them.  It's on my shopping list.  I am assuming it connects a load at the plug between live and earth which runs a selectable current of less than 35ma and consequently trips the house RCD.  That is the test you want.  Something which when you plug it into the wall trips the actual RCD on the consumer unit, rather than lighting up an LED on the device to say "its good"

The 2nd version - the "its ok light" I am buying in the UK on next week (because I can't find one under E300 in France).  It DOESNT trip the house RCD's (because lets face it, its a pain when all the electrics go off and have to be reset).  This is called an "earth loop impedance tester".  What it does is send a tiny test current between live and earth and measure it - and from that it calculates the implied impedance between live and earth.  The current is tiny enough not to trip the RCD's.  But it works out the loop impedance.  That is what all French sparkies plug in (that I have encountered).  In the UK my sparkie client tells me that they do the test on the input side to the consumer unit.  This is because we often have a lower impedance earth from the electricity supplier in the UK and so it doesnt muddle the measurement by measuring the impedance of the household wiring (a separate test).  Here I guess they figure they are only trying to make sure the sum of the 2 impedances is below 100 ohm and so its perfectly acceptable to measure it at the socket. If you know what the supply impedance is (with my UK sparkies measurement) then you can work out the impedance just for that socket, and detect faulty sockets (detached earth wires etc). 

However, that will tell you the impedance between the live terminal and earth and not check that such a connection trips the RCD.  It will read the same for a socket in the wall as it will for a socket on a transformer (BPS, regenerator , bog standard transformer).  Because it is measuring the impedance between the live wire in that socket and earth - which is a "through earth".  It is not checking that if you allow a current to flow between the socket live and earth that it will also cause a current to flow through the RCD live and earth.  Well, obviously it wont - because the transformer isolates it.

Be careful - not all tests are what they seem to be.  For example - if I press the "test" button on the RCD on the consumer unit in my office, it trips that RCD.  It doesn't trip the RCD at the main board in the house.  (well, not yet it hasnt).  I hope that tells me that the earth in my office has an impedance of less than the value needed to trip an RCD in spite of me building a patio over the earth spike, and that is why I am reasonably chilled about the French sparkie taking over a week to come out and test it for me properly.  But that test should have caused a 30ma current to flow between live and earth in the office.  That should have caused the same current to flow in the house on the main RCD.  Of course - its a race to see who trips first, but to date the office one always wins.

I have revised my illustration.  Red is the earth loop impedance test, measuring Z between live on the secondary and earth.  Note that is not the same thing as seeing what happens when a current flows through the green connection.  The green connection will trip the RCD.  The red one won't, although it may achieve (and should achieve) a result of Z<=100 ohms.