Although the 29A was the first route to feature the SG class bus, I actually travelled on one on the 37 first. Phibsborough Garage allocated their SGs to this route although they have also appeared on the 9 and 122.
The current 37 routing began on the 31st October 2010, or at least most of it did. This route had the most protracted birth of any Network Direct route. Initially it and the 38s/39s and 70 were to terminate on Wilton Terrace but that was delayed so all routes terminated in Burlington Mews. The 37 finally made Wilton Terrace its terminus in April 2013. Furthermore, under Network Direct the route was to terminate in Blanchardstown Shopping Centre, but it did not reach there until April 2011.
The route is not the direct route to Blanchardsown but instead serves all the places by-passed by the 38s and 39s. It spends a lot of its journey skirting the northern edge of the Phoenix Park before reaching Castleknock. From this point on the route gains a new lease of life, as it starts to pick up people from Castleknock and Carpenterstown to bring them to Blanchardstown SC. In Castleknock it briefly meets the 38 while in Carpenterstown it is joined for a while by the 239 which is always going in opposite direction to 37! (The blog explains this in detail)
As the bus route nears the city in Stoneybatter it takes a split routing uique to it. Outbound it serves Prussia Street, along with the other Navan Road bus routes. But inbound it serves Aughrim Street. The narrowness of the street probably explains why it is not served in both directions.
If you are not in a hurry to get to Blanchardstown, then I highly recommend a trip on the 37.
On the day I travelled on SG 14.