There is one thing to note with the Flamers: the little tentacles that come with the kit are very fragile, and can snap when being cut from the sprue. Take extra care with those.
This, as you can imagine, is much better than buying multiple blister packs of the old metal ones. The new models feel and look slightly on the smaller side, but GW certainly hasn't skipped the details. They've taken on a more 'classic look', taking references from much older versions.
As you know, I'm a Thousand Sons player, and thus I don't have much use for plaguebearers. But the attached dark magos I'm working on can and does. Therefore, I intend to create a set of 'plague-servitors': mecha-daemonic entities which, once finished 'altering' the host servitor, serve the magos' will.
Both of these kits are great additions to daemon players, and both have had improvements made, which put them above the predecessor kits.