Leatherette (eg, vinyl / synthetic leather) has been around forever and is used quite a bit in European vehicles in particular (BMW). Properly diluted auto-appropriate APC works great for cleaning this surface. Meguiars APC is great but even better IMO is the Optimum APC (OPC). I prefer not to use more general household type APCs.
To use OPC or Meguiar's APC, dilute it 10:1 (H20 to APC), toss in a spray bottle, and you have a great interior cleaner for your seats. For a real deep clean, which is probably only needed annually at most, I haven't found anything that beats diluted OPC with a bit of dwell time and agitation, some steam, and a final wipe. The same process works beautifully for carpets, floormats, etc.
I only use 10:1 OPC maybe once every couple months...I can usually get away with just a little diluted ONR in a spray bottle and wipe the seats down every time the exterior gets washed. Even better is to apply a protectant like Optimum Protectant Plus every 4-6 weeks. A little goes a LONG way and it really does help reduce abrasion as well as provides stain resistance.
Bottom line, I say buy a gallon of OPC. Its worth it. You can also dilute like 3:1 or 4:1 for heavy duty cleaning on the exterior, such as caked on dirt, tires, baked on brake dust, etc. Its a great product and COMPLETELY safe short and long term for pretty much any auto surface (wouldn't use on alcantara, as an example).