it is my belief that most turnkey properties under estimate capital expenses. I believe in low cost markets capital expenses will exceed $200/month (in a today's dollars) on any SFR. I use $400/month is So Cal for SFR cap expense ($300 on multi units which in my case are both smaller and share certain items (such as roofs, foundations, plumbing, etc) reducing costs).
So make sure you are going to get a top property management company and make sure that the capital expenses used in your cash flow calculations are conservative. There are quite a few forums/blogs dedicated to capital expenses and property management.
If you can get both a top property management company and the cash flow you desire with conservative cap expense estimates then you may do great with turnkey.
You will, of course, not be able to obtain the instant equity that can come with doing your own rehab. Also in general the property owner will be more diligent property manager than a property management company but the inexperienced diligent property manager may still make mistakes (such as not thoroughly screening tenants) as part of the learning process.
So I believe turnkey can work but like every large investment you need to do your research to verify it is likely to be a good investment (research capital expenses, the property management firm, vacancy rates, local economy, ... - everything).