A tremendous card, way better than it looks.
First off John & Jessie Burke feature a beefy tank and they are very much expendable, this is one of those allies that you use twice or so and then are happy to tank damage and horror with before refilling the slot with a different ally. This of course gets expensive so the active ability better be good, which it is.
The ability deals automatic damage, auto-damage is always terrific, weakening enemies so that smaller weapons or just your fists might kill the enemy in one hit, not to mention the luxury of combining damage and movement. Furthermore, this ability allows you to bypass the Aloof keyword, that's a terrific bonus for certain scenarios (and campaigns, right dude?). Every campaign has Acolytes at some point and other 1-hp allies, John & Jessie Burke make a mess of these enemies.
If you want John & Jessie Burke in your deck and tend to do "full-campaigns" with the side scenarios added (as I do), consider doing their scenario before you do Rougarou, their ability to deal ping damage makes a variety of challenges in that scenario outright hilariously easy, not to mention to engage and kill the mutt easily.
In short, John & Jessie Burke boost survivability and your ability to react to enemies around the map.
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Obviously, like Monstrous Transformation, this card is best suited to specific deck types and my recommendation is to try and get this card into an ally based character who juggles Beat Cop, Venturer, Dr. Milan Christopher and other 4-cost characters with Calling in Favors. In this case John & Jessie Burke just become part of the rat-pack that you lug around.
In the absence of Calling in Favors John & Jessie Burke are still great in a deck that has just 1 ally in it, for example 2 copies of Beat Cop or 2 copies of Peter Sylvestre. John & Jessie Burkes's tendency to die away eventually means that they will greatly expand your survivability while you wait for your planned ally.
Finally, if you're a you'll probably consider Well Prepared at some point and John & Jessie Burke synergize wery well with it.