I agree with our brothers on RD.net -
For now, the smart money is either with the Blinder M45 J16 revision, or, alternatively, with the Laser Interceptor.
Yes, "integration" is nice, but jamming capability should come first, and in terms of price-for-performance, the ZR4 is playing a catch-up game.
Furthermore, if you do bring the rear head to the forward playing field in an effort to beef-up frontal performance, you'll effectively have cut in-half the benefits of "integration" - the all-important directional threat display will now be nullified.
The LPP and AL G9 are also options, but I would reserve their purchase (read: I'm withholding my recommendation) until such a time that individual hobbyist groups here, Stateside/North-American, have demonstrated these devices' ability to, conclusively, jam the Stateside variant of the LTI TruSpeed.
The ZR3, particularly used in "enthusiast mounting" mode, with the rear head up front, may be a decent price-for-performance bid, particularly if you are capable of finding a second-hand/used unit at significant discount, however, with that, you'll need to consider both its age as well as condition, as out-of-warranty servicing, if-necessary, can easily
eat into the dollar margin.
I would not place any faith on being able to pass off *ANY
* of these devices as either parking-assist devices (for which the LI, LPP, and AL currently already carry this ability) or to try to explain to the road-side enforcer that the unit is in "receive only" mode (such as with the ZR3/4). That will be something that you'll need to take up in-court, but at the roadside, it's virtually impossible, realistically, to "talk your way out of" an enforcer seeing the unit as anything but what it truly is.
To think that an enforcer in a jammer-banned area won't know the Bel/Escort name is simply being too optimistic and bordering on naive.
Similarly, the AL and LPP are constitutively "jammer active" devices - and while the subterfuge may hold for less-experienced enforcers, for the more experienced ones, it can be a point of contention and may further escalate the hostility/threat-level of what would otherwise have been a routine traffic enforcement encounter.
Ironically, the LI may well give you the best-chance of being able to evade such probings by utilizing the RS-232 port as a physical "jumper key" that will completely disable the unit's jamming capabilities. With the key removed (which, given its size, can be done easily and very, very discretely as long as good attention has been paid to the tactical implementation of this task), the unit simply functions only
as a parking assist device.
But even then, an enforcer could well still say "tough titty, little kitty" - and you'd still be up a stream, proverbially speaking.
In all honesty, if you worry about the legalities of the unit, it would either be best to simply not use it at all or, alternatively, utilize some fashion of "quick disconnect" to at least conceal the external heads within the vehicle's bodywork so as to just not bother the enforcers to begin with.