Regarding disposers:
A few years back, Insinkerator, in their infinite wisdom, decided that a plastic housing was better than the old aluminum housing for the Badger disposers. Soon after the change, I began getting calls for relatively new disposers with a hole in the side. A penny, or some other object could be thrown by the impellers, bursting through the side. This wasn't impossible to do with the older aluminum housings, but it was rare.
On the other hand, the aluminum would deteriorate over time and crack or dissolve, particularly at the seal, which was necessary to hold up the disposer, and the outlet, which was necessary to keep it from leaking. Plastic eliminated this disintegration, so perhaps it was a good trade-off.
But you can't go wrong with a stainless steel grinding chamber and parts. Buying a better disposer is a good investment and should provide a better feeling of security.
A note on how disposers work:
The whirling turntable with the impellers, which are moveable, does not cut anything - rather, it throws it up against the sides of the disposer, where the actual cutters are.
Damage can occur if something is dropped into the disposer that it can't handle. The motor shaft can be bent, making the unit worthless. The bearings are not invulnerable. For those who do canning - remember to not put boiling water into your plumbing system. Whenever you dump hot water from a pot or pan, run cold water with it to prevent ruining the rubber seals that protect the bearings. Otherwise, you can destroy a disposer quickly.
An end-outlet tubular waste, or disposer waste, has a tee and within it a baffle. Often, if you force things through the disposer too quickly, such as celery, it will clog at the baffle. The purpose of the baffle is to prevent water that is forced through the tube quickly from coming up in the other sink. It is necessary.
In addition to a quality stainless-steel chamber and grinding parts, it is good to have a little more horsepower. I never install the Badger 1, which is underpowered. The Badger V is a 1/2 horsepower, and I install a lot of them because they are inexpensive. I have a 3/4 HP Insinkerator and it definitely does a much better job.
In addition, most higher-end disposers have an auto-reverse feature, which means that every time the disposer starts, it runs in the opposite direction, possibly freeing items that have gotten stuck under the impellers. Hence, they are more maintenance-free.
The Insinkerator company manufactures the bulk of disposers in the U.S. Contenders are Waste King, Whirlaway, Eastman. Perhaps a few others. Eastmans will reputedly mount to an existing Insinkerator flange, but I'd replace the flange if I were doing the work.
I hope this information helps.
BTW - avoid pouring aquarium gravel into disposers. Really not a good idea.