A B757-200 Captain reported noticing deficiencies in the new life vests that will be replacing the older design; including single chamber vs two chamber; no infant vest available; and no backup inflation tube.

Narrative

During my [recurrent training] we were shown new life vests which [my airline] will be putting on its airplanes. They have a single chamber; and a single strap which is wrapped around the body and a plastic clip to connect the strap. I did not notice whether or not there was an oral inflation tube on the new vest; but we were not told of one; nor did I observe it. We were told that this was being implemented to save weight. I am extremely concerned about this reduction in safety. Two chambers are important since; if one fails; the other will be available. If one fails with the new design; the passenger or crew member will be left without any flotation. We were also told that the infant life vests will be discontinued; and the parent must figure out how to place an infant into an adult life vest. The instructor also said that infants will not be held in the adult vest and will fall out; or float with their face under water and be killed. Why are we compromising safety in this way? In the past; [my airline] went to the extra expense; and safety was important. Now it appears that we are doing the least possible and providing a life vest of marginal utility in order to save money; and perhaps based on the belief that they will never be used; and if they are; the fatalities are an acceptable cost of doing business.