This thread gave me the confidence to spend the money on a Stacker/Destacker, and I just wanted to report my postive experience here in case it helps anyone else.
Just over a year ago I fitted a pair of dishes (one fixed, one moving) for my first satellite experience. I thought that a pair of feeds would be enough (I bought a twin-tuner PVR), but I was far-sighted enough to run a third cable as a spare. These cables were run very neatly by taking apart my plasterboard-on-studding walls, a job I certainly did not want to repeat !
However, a year later and I'm a lot wiser. My first PVR (near the top of the Topfield range) was returned as somewhere between "disappointing" and "useless". I now realise there is no single PVR that does everything I want to do, so I now have two, therefore four feeds would be best, but of course I ran only one spare co-ax.
Happily, as I ran the cables myself I know that it's (equivalent to) CT100. Also the length that has to be "shared" is only about 6 metres. So I guessed the stacker/destacker would do the trick for me.
And it works just fine, it looks just like two cables to me. I'd like to tell you about whatever signal loss there is, but the signal strength meters on the IPBOX9000 are not really very convincing, I think the readings are faked ! But all channels seem to come in just fine (and I took the trouble to check the extremes of the frequency ranges).
On one retail website I found a warning that the Johannsen stacker must never be used with less than 7 metres of cable, but I have bought the "Global Communications" unit and it doesn't seem to mind. However, many websites warn that the Global stacker must not have a wallplate in the common cable run. The instructions with the unit are a bit less rigid, they say you must use a "stacker compatible" wall plate (but no further explanation about what a "stacker-compatible" wallplate is). I am using a wall plate of home-made construction (a double-ended F joining connector and a right-angled adaptor behind) with no problems.
The power supply draws about 9W (a bit more than I expected) so you might want to consider switching it off when not in use. In my case I also use a "Homeplug" network adapter which is responsible for 4W of load, and your average V-Box positioner has a crude power supply that drains about 7W whether you are using it or not, so all the more reason to turn them off when not in use. For timed recordings the "Standby Saver" (Google this to see what I mean) in its USB form could be suitable to turn all this stuff on and off automatically.