Biggest issue I have with speedify if not being able to use my own server... You can get a dedicated box from them, but it's 100$+ per month on top of the standard plan... And it's still managed by them... I already have my own hardware, and if I wanted to use this for business purposes, my legal and security teams would not approve it being managed by others... I have had good results bonding multiple lte connections, but using my own server would make it a lot better...
Yes, speedify has a lot of smarts around packet loss. It uses up to 8 TCP connections in parallel to avoid slow downs based on loss.
But for the kind of burst of massive loss you describe, I'd suggest having a secondary connection it can use that during the bursts of loss. A cellular connection could be used just during these times to smooth it out.