I've got lots of thoughts on it.
First, I actually like Cameron, always have, always did. He took the opposite position on the 2016 referendum from me, but unlike Boris I'm pretty confident he took his because he geniuninely believed it.
His return to government, I think, is in many ways a positive. Sets a very different tone to have Cleverly and Cameron in post rather than Cleverly and Braverman. He's clearly got the chops for the job and using this story to blow Braverman's departure out of the water I think is a good move.
The big negatives are that he's in the Lords which can easily be used against him and that his presence damages the position Sunak took promising to be a new government. I think the charge of desperation levelled at Sunak is a bit strong, but he had to do something to shake things up.
FWIW, I don't think it will "work" in the sense of changing the electoral prospects of the Conservatives, only rapid economic improvement could achieve that and I think it's very likely that it's too late, even for that.
David Cameron left Parliament in September 2016. He did not execute the people's instruction from the Referendum, as I'd consider was his duty as PM. However, he didn't after the Referendum, vote to delay it's execution or override it with his own preference, as so many of his fellow MPs did during 2017-19 and that's more important. MPs who voted against delivering Brexit in the 2017-19 period I reserve my ire for. I hope Cameron has a big impact on the government because I like his politics.