A good question Todd . . . .
As you will see from this website, lapVent is a pretty unique product; the only roof ventilator of its kind to comply fully with all BS and EU directives for roof ventilation - in fact it surpasses requirements!
Opening up the lap of any insulating underlay without added protection, is without doubt a very risky option; storm driven snow and rain penetration, destructive wind uplift risks, wildlife infestation, etc. All add up to the dangers of likely structural damage and decay in the not too distant future.
A roofs insulating membrane not only controls heat/energy loss, it also protects against outside contamination, for instance; the ingress of moisture from the weather, even from steaming roofs as they dry out in the sun, the dirt and filth from everyday living, destruction from the birds and the bees and other things with little knees - the list goes on.
If unguarded breaches in the underfelt were deemed ok, then poking a bit of stick or a length of pipe down into the overlap would do the job equally as well - but beware, be very aware, trouble may not be so far away; and you may not always see it coming!
As with most everything - \'you get what you pay for\'.