On gas you will get away with this not on water, because of pressue ,not alot in gas but a dam site dangerous ,tested on manometer before just on fluxed joints, holds lovely , scary stuff Bill
Scottish gas are fitting them as standard, or supply and fit for about £200.yes they are good because powerflushing is not all it is cracked up to be .When installing a new boiler into an old systemyou should flush it but if you chemical flush only the old system,and empty hot ,when refilling...