I see you already have a FlowVis, that's what I would have recommended.
I suppose it would be nice to be able to monitor your filter pressure from afar, but I'll only caution you this: if you get that working, don't let that be the reason you don't monitor your equipment pad, in person, while the pump is running, every day. You should get into the habit of walking past your pad daily. In about 15 seconds you can check for leaks, check the filter pressure, check the flow rate, check the contents of the pump basket, and listen for any abnormal sounds. This on your way to your pool where you check the bottom and surface and walls and water for anything that's not supposed to be there, check the water level, and a quick peek in the skimmer(s) to make sure they're clear and not full of something bad (like a dead animal). 45-60 seconds a day, which you can call "pool enjoyment time," to ensure you don't let a little problem get by you that can turn to a much larger, more expensive one, if you ignore your pool for days or weeks at a time.
A pressure sender won't give you the full picture... One or two on your system might be a type of "early warning" system, for some problems, which would be cool, I suppose. Personally, I wouldn't go punching holes into my PVC or pump to add one. The one I have on my filter is one too many potential leak points as it is...
I know you only need one FLowVis, a second one wouldn't give you any additional data, flow is constant throughout the system, and two would always read the same. Pressure would be different, I suppose, depending on where you installed them, but I'm not sure you'd get any useful additional data from a second one. If something was to affect your flow (like a clogged up pump basket), then I would think all pressure gauges would move. Not in the same direction or by the same amount, necessarily, but enough to let you know something wasn't normal, and requiring your attention. I don't think you can have a spike in pressure at the pump, and not have that change the pressure everywhere else. Which would mean you'd really only need the one for the filter. Granted, pressure sensors throughout your plumbing could help you quickly pinpoint the area of a problem, but I'm not sure the effort to install them, and record their data for comparison, and then to track them constantly, is going to give you any great ROI.