condensing multipoint water heater savings?

[chorisia]

I have two brittony 11 multipoint gas hot water heaters in my house in multiple occupation probably will last another ten years based on previous experience. I find that Flexiheat offer a condensing multipoint SFK/SFK which will cost a third more than an alternative non condensing replacement any available multipoints now have powered flues, so whatever chosen will need an electrical connection. Is the gas saving of a condensing heater likely to be justify the extra cost? The alternative is to keep the Brittony 11 going when the gas water unit eventualy fails costing £300 to replace normaly these heaters are writen off at this point. Advice appreciated