http://kbmagic.com/ukcointricks.html this site should help.
a regular flipper will not sit open on a table or hand but makes for some spectacular vanishes think of it like a venus fly trap.
a gravity flipper is opened by gravity

can sit on a hand or table without jumping 15ft in the air and vanishing.
a magnetic flipper depending on the type ie strength can be tossed between hands without fear of premature opening

most good ones like the oxf's and next gen flips require another coin to open them.
a split / clone coin essentialy replaces a gravity flipper and can be shown seperated one in each hand etc, a DF'er will replace a slippery shell / copper silver coins.
a T.U.C. replaces a flipper and a slippery shell and the copper silver version will do everything the DF'er can......... for legal reasons I must state a tuc is neither a slippery sam or flipper combo or a scotch and soda, although it will do all thease things....... it is a totaly unique design........

gin and tonic anyone.
persoanly I'd go for a clone coin 10p or £2 version and get craigs dvd split happens for more rutines and a fancy mentalism effect.