I really enjoyed this review - thanks for posting it, I must get round to reading Gentles's book soon.
On the subject of Cromwell and the junto, I don't think it's disputed that he was involved in its fringes during the early 1640s. His links to Oliver St John and through that to the circle around the Earl of Warwick and Viscount Saye and Sele are well documented. Where historians disagree - and ultimately the evidence is too slender to prove either way - is quite how much a part of the circle he was.
It's possible to see his interventions in the Long Parliament in 1640/41 as naive and over-reaching, misjudging the politics of the day, but equally they can be represented as Cromwell flying kites for the junto in full knowledge that they might get watered down (but recognising someone needed to start negotiations).
Personally I think Cromwell's involving in freeing John Lilburne points more towards the latter, but whichever interpretation you take it's clear Cromwell was only a minor player at this stage.
John Adamson is good on this in his chapter on Cromwell and the Long Parliament in John Morrill's "Oliver Cromwell and the Puritan Revolution".