Have a Shimano external bottom bracket fitted at the moment, but it's developing an alarming amount of play so need to change it.

Given it only lasted a year, is there any benefit in replacing it with a more heavy duty one? Looking at the Raceface Diabolus – same price as the Deus and has blingy gold cups to top it off. I have the Evolve XC cranks, so assume it'll fit.

Do you need special tools to change one of these?

As I gather Raceface external bottom brackets haven't lasted well in the past. They might have improved recently though? Otherwise look at Acros or Hope's offerings.

For fitting you'll need one of the big spanners that fit the indentation s on the outside of the cups, like this:

http://www.chainreactioncycles.com/Models.aspx?ModelID=3784

If you can live without the bike for a couple of days, i would send the cups to sideways cycles and get them to fit the philwood bearings. I had mine done about 2yrs ago, not touched them since, much better than the raceface one which creaked from very early on before dying after 9 months. It was only £35ish

Another vote here to avoid RF, cranks are good but BB bearings not good enough. Try Hope.

My RF BB has lasted 8 months before it developed some play, SLX one a year and no worries so far

Get your bb faced and chased. It's a perquisite to running external bbs.. and never ever buy a raceface one.