A 56 inch long whip can only behave like a 56 inch whip. This is a basic law of physics. What the Miracle Whip (MW) and its derivatives do is match this whip on the HF and VHF bands. With a decent ground or counterpoise wire the MW may be only a couple of S-points down on a “decent” antenna on the higher HF bands. They work reasonably well and, in the past, I used my MW quite a bit, even from indoors. They are definitely NOT a miracle antenna, although they are not too bad. Since the owner, a Canadian called Robert, died there have been a few newcomers in the market.
Would I buy one today? Probably not. I have had better results with small loops. As a simply deployed mainly RX antenna they make an ideal companion for an FT817 or similar. Their beauty is their simplicity. If you want optimum performance in a small antenna there are better solutions. Small loops seem to work better, but then bandwidth becomes very narrow although loops don’t need grounds or counterpoises to work well. Personally, at QRP levels I’d use a loop every time.
As Wheeler showed years ago, efficient small antennas are reactive and unless losses are minimised, efficiency suffers. This is a fundamental limitation. Although high permeability ferrites and high permittivity ceramics can help to alter the size of space near an antenna and “magnify” the effective size of small antennas, the effect is small unless there is a lot of ferrite with high permeability or a lot of ceramic with a high permittivity. In theory, a tiny antenna can be very efficient but you’d need superconductors and lossless capacitors! At the moment, sadly, neither are practical to mortals!