I predict we are going to see this changing, and soon. This is the first edition of Shadowrun in which synaptic boosters are available for new characters AND in the core rulebook. In the past, their availability was too high and you tended to not started with so much nuyen. Wired reflexes used to be the only option, and they were definitely worth it. Now, with the boosters being in the reach of a character with priority A in resources (such as most samurai), and with alphaware rating 2 reflexes having an availability 14, we can expect to see synaptic boosters become the norm for street samurai.
That being said, the cost of synaptic boosters can still make them attractive to someone who neither needs a lot of essence nor is a combat specialist, but would like a boost to their initiative. I have a rating 1 system on a combat decker I just made, and it's certainly worth the money. The nearly 40,000 nuyen I saved by not springing for synaptic boosters allows me an additional level of cerebral boosters as well.
Also, the fact that it can be stacked with reflex boosters (something no other type of augmentation is able to do) means a new character focused on his reaction stat could spring for wired reflexes 2 and reflex boosters 2 to start with a reaction score of 9 (the cap for any metatype). It would still be a questionable choice, but some people might go for it.