If you don't intend to repace your TX's antenna, don't do it. You'll loose half your power for a less rugged antenna. Even then think about it a bit before you do it.
Most 2.4 control system RX's have linear polarization with diversity, with the intient that you mount one perpendicular to the other so you have both linear polarizations listening. Since it's just a flat wire -- in most cases these days both are sticking out at 90 degrees from each other in a pack-o-gum sized box -- it's easy to accomplish this, almost becomes foolproof, and takes up almost no extra space. The advantage of this is durability . . . I can bend my RX antenna and all I have to do to repair it is lay it flat again.
CP antennas are much better at being insensitive to orentation -- a right hand circular wave will always be right hand circular on a direct path -- and are really good at rejecting reflected signals -- a right hand wave switches to left hand on a bounce.
Nice advantages, but nothing is free. Your anteannas changes from rugged tiny wisps of wire about an inch long to a tangerine sized geometric shape that needs to hold that shape -- dent it in a crash or hangar rash and it's almost better to build a new one. It's easy to hide a wire. It's *usually* easy to hide a 2.4Ghz cloverleaf antenna in a 5# airframe . . . but in a 2# plane, things are getting really tight. 1#? 1/2#? Not gonna happen. Hard enough to get the rest of the electronics in there, or squeeze in a tiny fragile 5.8Ghz cloverleaf antenna, an antenna the size of a 2.4Ghz cloverleaf becomes a luxury most can't aford.
CP antennas provide priceless traits on a video link, but if you've got good polarity diversity on the RX, they're far less important on a control link -- just not worth the cost.
. . . and swapping between them isn't free either.
There's a 3dB power cut if your TX and RX are not both the same type -- if either one is linear and the other is circular you automatically loose 40% of your range. That means if you change your RX, you should change your TX too . . . but then you'll need to change *ALL* of your RX's as well.
There is also the part-15 concern (although this is minor) -- the part-15 certification on the TX (so you can operate the radio without a license) depends on the TX and it's antenna be paired with sufficient effort form the OEM to ensure it's not modifiable by the user. Typically, OEMs do this by direct soldering or putting on wierd connectors (ever wonder why there's SMA vs RP-SMA? SMA was a standard but RP-SMA wasn't, so it was used for this compliance). As a clever guy it wouldn't be hard to get past this, but you'll be breaking this certification. It's now on you to ensure the antenna you've just made maintains frequency . . . again, this is a minor quibble (since homebrewed gear can be coverd under part-15, but YOU have to ensure compliance) and the likelyhood of getting in touble for this kind of mod isn't really even slim.
