But wouldn't metal, a good conductor, work better?
I agree that glass isn't the best choice, in fact as someone who adds some level of conduction to everything I don't have any glass bowls accept for one, a Taroma 360 glass bowl. When I use** (used I haven't in a while) my 360 with the glass bowl, I used to heat soak the herbs in the glass bowl as the thing took ages to heat up and didn't really add the conduction I wanted unless it was heated for like a minute. I got the T360 titanium bowl and you just put the diffuser on and start to draw as by the time you take your second breath the bowl has heated up and started to conduct to the herbs.
So metal is definitely the choice for conduction over glass but if you put the time/calories in, you can use glass, I just personally don't think the effort and the loss (heat soaking and loosing terps) is worth it when using glass as it takes so long to get meaningful conduction. I wouldn't recommend it... or even advertise it as a "feature"... unless there is an expectation, like with the T360 that you "heat soak" the herbs in the bowl to also heat the bowl to add conduction.
Most people using a Freight Train or Thermal Twist will have finished the bowl before the glass heats up enough to to really add any value from a conduction perspective - I never could get through a bowl without having to stir the thing on the Freight train using a glass bowl.