Compatible toys
In general, you can use any toy that's directly powered with USB. If the device is charged with USB, it's incompatible unless you manually rebuild it.
Also note that if the toy has a remote on the cable, then it's not going to work unless the remote is analog. However, most cheap toys with a remote can be reworked into a VibHub capable toy with a pair of scissors (note that this is a one way conversion).
Toys that work directly
These are toys that are powered directly with USB. They're a bit of rarity these days. But if you can find one, it's by far the easiest option.
Toys that are easy to use with the screw adapter
Using the VibHub Screw Adapter or VibHub Wago Adapter, these devices are budget friendly options. Note that in order to use these with the adapter, you have to manually cut off the wire, strip the end, and screw it in place into the VibHub adapter. This obviously ruins the use of the original remote control, but these toys are super cheap anyhow.
These devices are super cheap (usually a few dollars), and can be turned into a VibHub toy by cutting the power cord at the base of the remote, stripping away some cord, and using the VibHub Screw/Wago Adapter. You can find them everywhere on sites like Amazon & AliExpress. Just search for usb vibrating egg or similar.
Toys that can be used, but require significant rework
Some vibrators with a built in battery and are USB-chargeable can be reworked into VibHub toys. However, this process involves opening the toy case up, taking out the existing circuitry, and soldering the charge port directly to the vibrator motor. This requires significantly more work, but if you're comfortable around a soldering iron and basic circuitry, you'll have an easy time doing so.
Toys that are NOT compatible
Toys that don't rely on 5V (or thereabouts), or that are already wireless cannot be used.
Note: Technically you can rework an already wireless toy by taking out the existing circuitry and soldering the motor to the charge port, but doing so is a destructive process, and using a simple toy listed above with the screw adapter is going to be much cheaper and easier.