Short Summary...
PLB = $50/year for battery replacements, best in emergency, hope you never have to use it.
Spot $100/year +$10 for batterys, Send Ok or Help Messages, send 911 Message. Probably will work but not quite as robust in emergency as PLB.
Spot $150/year+10 for battery's , adds tracking, so others can verify your ok, or get an area to start looking you if spot is does not survive crash.
Example, Spouse sees plane has crashed on the news, goes to Spot Site to verify you are still flying and that it is not you.
You Decide which has the most value for your situation. Both gives you the most capability but also at the most cost.
Brian
CFIIG/ASEL