The problem is that it's not sensible; it's a fantasy of numbers that couldn't possibly work; but it looks attractive - which is all that matters for the voters who don't think.
As others have noted, the ECHR is not the EU. For several years now the lunatic fringe of the Tory party have pushed to try to reduce those rights from the UK justice system, and should (in my greatest nightmares) Reform ever grow strong enough to actually win power, you can be 100% certain that those rights would start to be eroded further. It's what fascist minds do.
I don't think anyone would consider people risking their lives (whilst being exploited by people traffickers) to be a positive. The issue is that our government have closed off legal routes for immigration (and underfunded the immigration service); meaning the only way left is illegal. Having created that problem, they then point to the scourge of "small boats" (complete with the usual anti-immigration fear mongering). Essentially they created the problem they use to scare you.
The right route is to have a properly funded immigration department, and legal routes for people to apply. There will always be attempts at illegal migration; you'll never stop that - but you would massively reduce the "small boats" if people had an alternative.
You can absolutely guarantee that Reform would not be the solution to this problem; they'll simply continue the same process, and ratchet up the fear and anti-immigrant rhetoric.