To Clear this is a Little Bit.
1. If you have a line6 interface(tone port etc with their bundle( and Not a Processor (podxt,x3..)
You Can ONLY use standalone unless you buy a ilok license for plug in separately.(not sure exactly if you have to buy the licence or entire setup, but standalone is surely free)
2.If you have a H/W Device (podxt,x3..)
You can ONLY use the pod farm plug in. The standalone won't work for you.
The plug in is free for x3 series users and xt series users need to buy a license.
Any model packs you already bought for xt will be enabled in pod farm plugin.
3. If you have both, you can only use what you have licensed/attached to be used with respective device.
....................... /
Charvelguy you can use standalone.
since you already have gold bundle with plugin i am sure you are entitled to the free standalone.
For vst plugin version you might need to purchase ilok licence as the vst requires either a hardware processor that is activated or an ilok license.
A Big TIP: For Podxt (hopefully podx3 too) users : You can clear a bank in you pod and set it up for use Just with the vst or you can just do all in gearbox standalone gui but record via vst, it will give you a dual pod series benefit,all without chaining multiple vst and hence much lower latency.
what i mean here is you can have some fx at input (i.e from the H/W itself), like you can have the tube drive and eq before the vst to shape the input your vst receives and can have other stomp or the devices along with other from vst. it becomes somewhat flexible routing setup.
The eq at pre works quite good in faking an acoustic or infact any signal with fx and shapers. The vst works on what it hears, and you can deliberately change/control what you want it to hear.

I Am A Man of Few Words Ironically Understandable by the Select Few, hence more often than not I have to Come out of my Manhood to do the obvious. Now Ain't it a cruel world?