To me it would depend on how comfortable I felt instructing in a twin with the minimum PIC required. If you are current and quite familiar with the twin and IFR procedures and flying/instructing single engine approaches, why not? Might be a little expensive, but what in aviation isn't?
If you have the knowledge and instructing ablilty, go for it!
One other thing;
How much of your time in the twin has been spent towards your MEI, what I mean is that as I did my mutli checkout I did it all from the right seat and doing drag-demos, Vmc demos and so on. Getting to know your plane really well would be key to passing a MEI-CFII ride.
When I was instructing I had a student doing both his CFII and MEI at the same time. However he did keep the training seperate. To keep it as easy and as independent as possible he did his CFII training with me and did the MEI with a coworker. He admitted the work load was high but successfully completed both the first time.
I know saving $$ is important, but the quality of instruction you receive is gonna reflect on how well your students do. If you rush just to get the bare min, you will most likely provide subpar instruction and thus have poorer performing students. You should not be trying to do this as a time builder only.
As for the one week wonder schools...My advice is to avoid at all costs!! I have met a half dozen or so instructors that have attended those schools, and having flown with some of them and some of their students, I was not impressed at all!!! I am not saying that all people that attend those schools are poor instructors but for the most part they give you training to pass a checkride, not to be an instructor.
Im convinced that failed checkrides do little in hurting your career future. Maybe if you have a string of failures and can't back it with knowledge at an interview then maybe it'll hurt. If you've learned from your mistakes and deal with it and continue to improve then who cares. If someone makes a big deal out of then screw em.
It makes for a long sit down with the examiner for the oral. Then like the others said it depends on your comfort with IFR procedures in the twin. It is definitely doable, but make sure you're ready for the long day.