Doing patent applications for a flat fee makes a lot of sense.  In setting the fee, the practitioner looks initially at the complexity of the invention.  Another variable, is the number of embodiments.  The number of embodiments is a delicate area because in general, as a practitioner, you want to encourage an inventor to disclose a reasonable range of embodiments.  All of the above means that the practitioner must conduct at least a partial interview before being able to quote a flat rate.  The practitioner also needs to provide some legal advice about the desirability of having a reasonable number of embodiments, and not limiting the disclosure to a single embodiment.

A flat fee automatically takes the practitioner's efficiency, experience and skill into consideration.  The practitioner should set the fee within the range that the practitioner believes would typically be charged by other practitioners of similar experience and skill for drafting a patent application of similar complexity.  If a practitioner is inefficient and takes more than the usual number of hours for such an application, then the practitioner must absorb the hardship of working more hours for less money.  On the other hand, if the practitioner is more efficient that the average patent attorney, then I can see no reason why the practitioner should not receive that benefit. 

What the flat fee does is it allows a fee to be set taking into consideration a range of considerations, including all of the considerations required by USPTO and state bar ethics rules regarding avoiding excessive fees.  Not all of those considerations are discussed here.  I have discussed the ones I feel are most pertinent. 

A flat fee benefits the client by providing predictability to the cost of the preparation of a patent application.  I think a lot of the complaints about fees in the legal profession stem from cases where billing by the hour leads to unexpectedly large fees.

There may be case where a flat fee is not practicable.  If the complexity of the application and the scope of the invention are not clear, then it may not be practicable to set a flat fee.  But, those are probably the exceptions.