I wouldnt fly without a PCAS or TCAS.
One aircraft I fly has TCAS, otherwise I always use my portable PCAS.
The decision came after a very close call and a realisation of how poorly see and avoid works, particularly in faster aircraft or in poor conditions.
The current PCAS system works very well.
After some thought I use the non directional unit.
The display is very clear and bright but more importantly the warning beep is clearly audible without the headset connection (although with it it is even better).
On the issue of the headset connection be aware that there are some older units still on sale which do not come with the headset connection. These units are out of date and you would be well advised not to buy one. Moreover they do not have the connector on the unit so even if you buy an adapter it si back to the factory for a mod.
Essentially (as probably explained in the afore article which I have not read) the unit "forms" a protective bubble around the aircraft of up to 5 miles and 5,000 feet.
At this setting (which I use) if traffic is within 1 mile and a 1000 feet you receive an audible warning which becomes more pronounced within 1 mile and 700 feet.
Personally I never look at the display. If I receive a warning it is then a quick check of the display to see whether the aircraft is above or below and whether the seperation is increasing or decreasing (the trend is displayed). I will adjust my height if the aircraft is a threat.
I have found it works very well. I have had a number of aircraft that I have only seen after PCAS and it is interesting within a controlled enviroment the way it mirrors TA (as you would expect).
One of the reasons for selecting the smaller unit is that it is totally self contained and battery life is good enough for the longest flight without a change. It is therefore easy to move between aircraft.
The directional unit requires an external power supply. It is possible to conenct to a battery if the ship does not have a lighter adapter and Zaon sell their own purpose made unit but that reduces portability (and perhaps the tendency not to bother to set up the unit).
On the other hand I have seen the system connected to a 496. The sytem so set up is impressive. If I were going to fix the unit permanently I would probably go for the directional unit.
Of course it is really important to understand the limitations. The other aircraft must be transponding so it will not see gliders for example. In CAS I have found it would not react quickly enough to deal with really fast moving traffic. It has limitations in a busy circuit because of the obvious proximity and volume of other traffic. It is really important to follow the instructions in the manual if you need to reset the unit or change the batteries in flight as there is an obvious gotcha. Finally, and needless to say, it is important to understand the reaction time you have after you receive an alert if the other aircraft is on a collision course - you need to do something about it immediately.