First of all: thanks Miguel for the seeds!
This is a new species that I had the pleasure of tasting today, it was cultivated from seeds for 3 years and gave its first fruits when the tree reached a meter and 30 cm high during this summer.
You can see in that photo two fruits on the right on top of a leaf and to compare I place two red strawberry guava fruits on the left. The flavor is different to this one, being more lemony and stronger. I would say that it is both more acidic and sweeter: deeper. The skin tastes like lemon guava and I enjoy eating it more than most of the skin fruits I know.
Other notable differences are: the pulp of the arazá serrano is yellowish while that of strawberry guava is white, the consistency of serrano is harder and less damaged when falling to the ground, perhaps less perishable but I doubt it. It is a taller tree that supports up to -7 or -8 º C, more rare and it should be growed to save it from extinction.