The rebates are all in the amount of $50, and indicate that the launch of these three Hotspots is imminent. Verizon currently sells two LTE Hotspots, and the newcomers will raise the total to five.
The Novatel MiFi 4510L and the USB551L, which is conveniently sized in the form of a USB stick, are both Mac-compatible, whereas Samsung's LTE modem is quite a thin rectangular device. It might also work for Macs, but not much is known about it at the moment. We will know pretty soon all the details, since the rebate list indicates they will hit the shelves soon. All are backwards compatible with Verizon's 3G network, and offer LTE speeds of 5-12 Mbps download, and 2-3 Mbps upload.
With the price of LTE being $50 for 5GB, and $80 for 10GB a month, you might be better off getting an HTC ThunderBolt (our LTE data speed tests with it here) while the $30 unlimited 4G offer is still out there, and then pay the additional $20 a month after May 15th to use it as a mobile hotspot every now and then, up to the 2GB limit. Verizon's current LTE modems cost $99 on a two-year contract after a $50 online discount, so the price for the three newcomers shouldn't differ much.
Thanks, Friendly Verizon Phantom!