The SDRuno software that is supplied with the RSPdx is probably better than any of the 3rd party offerings.
I have an RSPdx that I use with a home brew PA0RDT active antenna which is located in a corner of the garden, away from the house. The active antenna connects to the BNC socket and I have a VHF ground plane antenna on the SMA socket. I can use it with the main HF station antenna, via the RX in/out sockets on my K3, but it is more use in my situation to use the active antenna.
Incidentally, the active antenna has the power disconnected when I transmit on HF. The circuit is on my web site:
www.qsl.net/g4aonAn end fed wire is likely to pickup a lot of noise, it is better than no antenna though, but I would look to use an antenna that is less noise prone.
An RSPdx has less dynamic range than a typical ham transceiver, plus the bandpass front end filters are very wide, which can result in overload in some situations. You need to pay attention to the gain setting. For the money an RSPdx is quite good, much better than the very cheap dongles, but not up there with a more expensive SDR, such as the Microtelecom Perseus (only covers 10 KHz to 30 MHz though).
In addition, what else covers to beyond our 23 cms band for little cost and makes a good means to monitor, or record, your own transmissions?
73 Dave