While this is a bit of a revived dead thread, I though it worthwhile to mention another GCoder sender.
But first, as I'm sure many know, the Grbl Panel developer stopped supporting it about a year ago. For fans of Grbl Panel (like me), that was quite unfortunate. But a new sender has taken the place of GP -
ioSender (AKA GrblHAL GCode Sender).
Even though it is associated with grblHAL, it works quite well with "Grbl Classic". It is very similar in many ways to Grbl Panel but goes well beyond. It has a clean user interface. The 3D display updates in real time and is quite in sync with the actual spindle. It supports numerous connection methods - USB, Ethernet, Wifi and BT (if the Grbl Board supports it). Changing Grbl Settings is easy with all the bit fields broken out as check boxes and copious help info. The probing section is an order of magnitude better than any other GCoder out there. It has tool height support, edge and height finding, inside and outside center finders and height map probing. The height map probing also allows transformation of the loaded GCode program. Great for shallow etching of PCBs. Works for uneven surfaces in general.