This is OK in itself, but it's rather like Paul & Ringo borrowing a couple of younger musicians & trying to remix/re-record the Beatles.
That's partly why it's pointless.
The other part is that Clive Palmer & Mike Heron NEVER historically were the ISB. Clive & Robin Williamson formed it, Mike Heron joined last in 1965.
On the release of the first album, Clive contributed 2 or 3 tracks & was gone, followed by Robin, before Mike & Robin came back together later in 1967. So, there is NO period in ISB history or even their mythology where they were Mike n Clive & not Robin.
The 2 new people are an improvement on the unlamented Malcolm LeMaistre, I must be honest, but that's no recommendation. Don't waste your money-just savour the first 4 albums when Heron & Williamson were BOTH at their staggeringly highest points of songwriting,singing,playing,stagecraft and sheer genius.