Yes, twice.
Once:
BOSS-DS330 synth module, bought 2nd Hand, from America -- came with US issue wallwart. Didn't want to cough up 30 or 40 quid for an "approved" Roland UK adapter, and as it's an AC feed in (not DC), couldn't lay my hands on a cheap replacement. Ran it on a 240-110v autotransformer for a while.
Twice: Computer monitor -- 110v only. Ran that for 3 years through the same autotransformer (by now the BOSS had a proper, though still not approved, PSU).
There's 2 kinds of transformer.
Your regular "transformer" as found in most equipment has 2 or more windings. One faces the mains supply, wound to 240v, one faces the equipment, and can be anything from 1-50v. These are usually totally isolated from each other.
The other is an autotransformer. This is wound as a tapped winding. For 240v->110v, you apply mains across the whole thing, and put the load across the centre tap and one end.
For 110v->240v, you apply the mains across the centre and one end, and the load across the whole thing.
Think like a big resistor divider, but with no appreciable heat dissipation. The load is not isolated from the mains.
Side effects?
Don't overload it -- the voltage will drop, the thing will heat up, and may well just conk out. Note that a failed autotransformer may leave your equipment connected to nearer to 240v, if the "wrong" half of it fails. A transformer (isolating) won't do that.
Hum? Pay attention to earthing arrangements and you shouldn't have a problem. On mine, the earth goes to the metal body of the transformer, for safety earthing. Other than that, I had no problems, the earth just connects through as normal.
Don't use little noddy shaver adapter things. Get something meatier.
Your link didn't lead to a specific product, so I can't say about that.
