There was a rather large discussion on this exact topic. However, I guess I'll summarize.
Yes, it's a gimmick. However, there are some "perks" in comparison to using other materials (if you want a full explanation, go find that other thread. It involved "China" or something).
- Silicone (consumer grade) is relatively more environmentally friendly than other popular sex toy materials. HOWEVER, it's not environmentally friendly if it's not recycled in the end.
- Rechargeable batteries create less waste (in the short term) because they are rechargeable. HOWEVER, the energy to charge them obviously comes from somewhere, and often those sources of power are not very "green" (many people still use nuclear, coal, natural gas, etc.). Rechargeable batteries are also made with more toxic materials (often heavy metals) than regular batteries, and thus are not really too environmentally friendly if they are not recycled in the end.