Well that's exactly what they did. Settle down and stop looking for things to complain about. That is a fine job. More on reddit.com

"Fernco's", or unshielded rubber couplings, are ABSOLUTELY not acceptable for this application - they have no structure, so with a little bit of shifting, whatever cast iron there is above the plastic could come crashing down someday. No-hub couplings are for joining no-hub cast iron pipe and fittings. They are not rated for use for joining dissimilar materials (i.e. plastic and metal). They do not meet the ASTM standard. Mission or Pro-flex couplings are acceptable to use. They have a solid stainless band of acceptable gauge to use to have enough structural support for your purposes (going from cast iron to plastic). Here is the one you'll need to go from 4" CI to 4" PVC-DWV. However, if your cast iron is extra-heavy weight, and not standard service weight, you'll want this one . How do you tell? Measure the diameter of a piece of 4" PVC, and then measure the diameter of the cast iron. If the cast iron is the same as the plastic, it's heavy weight. If it's smaller, it's lightweight. I highly recommend just removing any cast iron above the new wye you're putting in. It's not great to have a ton of cast iron weight on top of a short vertical section of piping, for obvious reasons (although it IS allowable). It's just something that I personally think is not great, and I'll typically just put in a cast iron wye if I'm leaving the stack above it. Also, if you're cutting into the stack to add a bathroom, do you know whether or not that stack has vents tying into it below? If it does, then it's against all codes and you really shouldn't make that your tie-in point for a bathroom. Also, if the toilet below the new proposed bathroom location goes straight to the stack and the stack acts as that toilet's primary vent, then it is also against code to add a bathroom above that point and for good reason - you'll siphon out the fixture traps in that bathroom and your house will smell like a sewer and you'll allow pathogens into your home potentially. Also, to clear up a few things: -Fernco is a brand that makes all manner of couplings. Buying a fernco rubber unshielded coupling is not advised for this. However, the products I linked are Fernco-made products, but are shielded couplings rated for the purpose. Fernco has a superior elastomeric compound that their "rubber" is made of, and it is resistant to all kinds of chemicals and much more durable than their competitors (primarily Mission Rubber, which is another popular and a little bit cheaper manufacturer of similar couplings). However, Mission Rubber hasn't really had any advances in its product offerings over the years. More on reddit.com