I agree the Suunto M3 is a decent compass. Though to be fair, it has the same limitations as all the modern plastic body compasses marketed by Silva, Brunton, Suunto or Kasper & Richter (another good brand, but for some reason not mentioned very often).

The problem with most liquid filled plastic compasses is that the capsule might break or leak. It's not really a matter of if, but when. Mechanical damage, low temperatures, changes in air pressure are all contributing factors. To be sure, a compass is a precision instrument and should be taken good care of in the field. But stuff happens and my experience suggests even a high end modern compass made by a brand as reputable as Suunto can fail very suddenly and for no good reason.

The main problem IMHO is that the compass capsule is typically made of a relatively hard and brittle plastic liable to microscopic cracks (or worse). Then a bubble will form, at first maybe just a small one but it could grow exponentially at higher altitudes, maybe so much as to interfere with the needle movement. Alas, the Suunto global needle is particularly sensitive to that problem, it just doesn't seem to work correctly without liquid.

K&R has a different solution. They make capsules from a flexible thermoplastic, which expands or contracts depending on the outside temperature and air pressure. It is a sound concept and has been working just fine so far in my experience.

The Cammenga lensatic is an entirely different breed. I like it for what it is, and it is a very useful and reliable tool. Truth be told, you can navigate with a lensatic compass and map just as easily as with a baseplate compass, all it takes is getting used to a slightly different technique. The lack of adjustable declination is a disadvantage, but then again, many if not most "serious" compasses made for professional use lack that feature. Again, it's a matter of technique. You can always navigate by magnetic north if you don't feel like doing a little extra math.

Those who find the above beyond their skill would do better to invest in a land navigation class first. I have met a surprising number of people who bought a compass without really knowing how to use one, which they would never admit obviously. Maybe it's an ego thing but frustrating no less.