As my user name might indicate, I am a fan of the Theoben Rapid.
I will be the first to admit that it leaves some things out which many find annoying but on balance it is still a very fine air rifle.
I currently own 2 Rapids-one legal limit .20 and the other a FAC .22-and both are late model Mk 2's with the latest series 4 triggers. The legal limit one has a scalloped loading port which makes single shot loading very easy whereas the FAC one is slightly older and just uses a magazine feed . Mine also have pressure gauges screwed in to the base of the block. As the legal limit Rapid mk 2 is regulated as standard the gauge shows the regulator working pressure NOT the pressure in the air bottle so only shows when your rifle has gone 'off the reg'.. For those who want to know how much air they have left in their bottle, several after -market mods are available. As all of these mean that the bottle is moved forward they all require stock drilling which many find unacceptable.
The Rapids of whatever era are high quality rifles and will last a very long time. Some unkind shooters call them 'agricultural' and I don't really know whether this description is meant as an insult or compliment.
Comparing one with other precharged air rifles will tell just by looking that you have a solid piece of engineering which will give you many years of service with minimal maintenance being needed. Maintenance is easy and modifications are all too easy which gives rise to the comment above warning against buying a second hand one unless you know what you are doing.
That being said pretty well every fault seen in a second hand botched Rapid can be put right unless the block itself is damaged. In use the Rapid is as accurate as anything else. The barrels in regular use are generally of a high quality from leading German manufacturers. As most reading this will know the Rapid is what is called a 'bottle gun'-the air store is in the form of a 'buddy bottle' so called because its origins are from diving when a small amount of air is required as a back up or to help a fellow diver in trouble. No one can claim that they are pretty. I certainly would much prefer to use a tube preferably one with quickfill rather than having to remove the bottle for filling. Sadly these are not freely available so I prefer to use the 'MFR' type of 280cc bottle and valve allowing for much easier removal for filling than the standard 400cc and 500cc bottles. Some bottles have been drilled in the base to install a nozzle enabling direct filling but very few are available and many experts will caution against using this method on safety grounds. The absence of quickfill is regarded by many-myself included-as a disadvantage when the Rapid is compared with say the Daystate Air Ranger which is possibly the closest rifle to compare with the Rapid. If this bothers you then again after market modifications are available.
One thing to me which stands out when comparing a Rapid to its rivals is the ease with which tasks like changing barrels and calibres can be a carried out. It takes me about 15 minutes to change the calibre of my Rapid. On balance the Rapid in every incarnation from the first Rapid 7 (this term is only accurately applied to describe early versions where the 7 refers to the capacity of the magazine and the marking on the side of the block) to the latest Rapid Mk 2 made up until the demise of Theoben. For those wanting the very latest then I advise you to look into the products made by RAW (Rapid Air Weapons) in the USA which remedy all of the disadvantages found in Theoben made rifles outlined above.