Presume the 458 refurb includes: new carpet and seat covers, improved toilets and windows, to match 444 standards (just 1st class will have new seats)?.
Although the running gear has not changed much (other than the gearing), it may have updated control and customer route display software, so guess the refurb'ed 458 12 car will be tested on a test track at Widnes before the Waterloo - Portsmouth main line?.
Should not have the issues the 442s had, but there may be other unknown issues that may be found under testing?