I remember spending a fortune on Space Invader machines and was glad when this gadget came out about 3 years ago or so.
I mostly play Space Invaders on it, but the other games including Phoenix (shoot the birds), Qix (an upmarket line drawing entrapment game) etc, are worth playing. Buttons arranged so can be used by left or right-handed person, neat idea.
Good for children, as no pesky games costing £40 to buy, but it can lack the variety of the new game consoles. Just add some batteries, plug in and it's ready to play. If your TV is modern it plugs in either the inputs for a video camera (look for red, white and yellow RCA sockets) which I use as no spare scarts sockets on my TV.
If your TV doesn't have any of these, you can connect it via the aerial socket by using an RF modulator (try Maplin, but take the game with you).
Takes 4 AA batteries, although there is a socket for a 300mA 6v mains adaptor (£5 from high street), which will save money if played a lot.
Am not commenting on the price: about twice what I paid for mine, but they were available in the high st.