The risks are:
1. Unscheduled maintenance
2. Accidents / Dings
If you do the number crunching, you will probably find even without 1 or 2 above you will struggle to make the numbers add up because of the number of hours you will do compared to a school. If you are determined, lease back can help clock up the hours and so reduce the fixed costs.
If you choose a different type of helicopter with more favourable component times, you
may get lucky and have a run where nothing goes wrong and have some very cheap flying. Or you may end up with some very large bills if the previous person had that good run
Negotiate a very good deal with a school so you can toss them the keys at the end of the day and let them worry about insurance, maintenance, hangarage and so on. This also allows diversity in your hour building, both in location and type.