As well as the dedicated "London Wasps" branded reflinks (see above) I also have a cheapo FM earphone-only radio that has a FM range that starts at 60MHz (as opposed to the usual 87+Mhz that most radios start at). This works fine at all places I have tried it at (including Wasps. Twickenham, Lords, Edgebaston and The Oval), wheras altough the reflink works at all Premiership venues it doesn't seem to work at Twickenham and some of the cricket venues.
Any FM radio that has a range starting at 60MHz will pick-up reflink. However most start at either 64MHz or 87MHz so these will not do.
They are hard to find on ebay, but can find them easily enough on Amazon (The one I have is marketed as Greenbang on Amazon)
Advantages are: can be used anywhere, not just as reflinks, but also as normal radio.
Disadvantage is no simple switching between Reflink and commentry usually found on second channel of a reflink device.