I'll hesitantly say yes (because we don't really know what your issue is). The problem is we don't know how much it will have to rely on battery power to do so. A UPS is meant to ensure the connected devices receive acceptable power. If the incoming power is unacceptable and it has no other means to correct it, the UPS will switch to battery. Standby models are either passing incoming AC (with mild filtering, like a surge protector) or on battery power. Line-interactive models can boost/trim the voltage (to a limited extent), without using battery power. Online (double-conversion) units never pass incoming AC, always relying on their inverter to generate clean AC. They are generally very expensive and inefficient.
For most people, a line-interactive UPS should be plenty to solve common issues. If they're not, there's likely something seriously wrong with the electrical system/generation that needs to be investigated and corrected. I would suggest trying a good 1500VA, pure sinewave (NOT simulated sinewave), line-interactive model. You may be able to find something like this around $200. As I mentioned before, I'd buy it somewhere with a good return policy, just in case it doesn't work well for you.
There are some UPSs which have multiple boost levels and can boost voltage drops into the 90s. Yes, a line-interactive UPS can run in these modes continuously. You're right, a line-interactive UPS can't fix frequency problems, without resorting to battery power. A Kill-A-Watt will be good for diagnosing ongoing issues (continuously low/high voltage, frequency issues, etc.) but won't work well for picking up brief blips.
To me, that looks like a plain old power strip with fluffy marketing. A simple ferrite choke (or possibly even just a ceramic capacitor) is all they need to claim EMI/RFI noise filtering. I doubt this will resolve your issue.