In the first place, just buy your FRDM-K66 board. This has a built in OpenSDA debug probe which can be programmed with different firmware to provide either a CMSIS-DAP (for OpenSDA, generally called DAPLink), a SEGGER J-Link, or a P&E Micro debug probe interface for the IDE to connect to.
I'm not sure which probe firmware variant is shipped by default with FRDM-K66, but all are available for download from
This will give you the chance to play with the three firmware variants and see what you prefer. They all provide slightly different capabilities when used with the IDE - for instance the Live Variables functionality built into the IDE will only work with the CMSIS-DAP firmware.
This built in probe does have some advantages over a standalone probe - in particular it will generally provide a VCOM port back up to the host PC for UART like I/O. However generally the built in probe is slower than a standalone probe, and the OpenSDA probe hardware was not designed to be used to debug an MCU on another board (i.e. it can't be used once you have your own hardware).
If you decide you want to try a standalone probe, particularly once you have your own hardware, then probably the cheapest route- but the one that provides the most built in capabilities within MCUXpresso IDE - is the LPC-Link2 (http://www.nxp.com/lpclink2) which generally are around $20. This will also support the use of the SWO Trace capabilities built directly into the IDE.
But both SEGGER and P&E offer various price points for their standalone probes too. And do provide other software to provide other capabilities. See their websites for more details.
Anyway for more details of using each of the various probe types plus their capabilities within the IDE, please see the MCUXpresso IDE v10.0.2 User Guide, which is provided as part of the product install and can also be downloaded from http://www.nxp.com/mcuxpresso/ide/documentation
As far as the Pro version goes, at least in the first place, there is probably little point - as the additional SWO functionality is only available using LPC-Link2 (with our own LPC-Link2 CMSIS-DAP firmware), as described in the purchase page at: MCUXpresso IDE|NXP
Regards,
MCUXpresso IDE Support