I've had no problems with a couple of low priced speed/cadence sensors, whether on the trainer or riding outdoors.

Regarding Bluetooth vs ANT+, the main advantage to ANT+ is transmitting data to more than one receiver device. Handy for folks who work with a coach or record to both a bike computer and phone, or laptop and other device. Bluetooth reportedly is easier to make connections and has a faster signal. In actual practice I don't notice much difference. My apps usually slow down the process of pairing Bluetooth sensors, while my ANT+ sensors are picked up almost immediately by my phone and bike computer.

XOSS: Among the least expensive of the earth induction sensors that don't require a magnet on the crank arm (cadence) or chainstay (speed). These are switchable between speed and cadence by removing an re-inserting the battery while watching LED light colors indicate the mode. These are Bluetooth/ANT+. Some bike computers and phones allow choosing between the wireless protocols (assuming ANT+ compatibility). My XOSS G+ computer appears to choose automatically. Works fine with both Bluetooth and ANT+ sensors.

Older Wahoo Bike Pack (if you can still find one). These were made around 2012 for the iPhone 3, 4 and 4s and included a case that added ANT+ capability to convert a phone to a proper bike computer with the Wahoo Fitness app. Obsolete now, but not bad even by today's standards. With the right app (Cyclemeter was better than Wahoo Fitness) it would do everything a bike computer can do... but in a bulky, heavy package with a battery that would last only a couple of hours of continuous use with the display running. I still use it but only for indoor trainer sessions.

But I still suggest it -- if you can find one -- because they included an excellent speed and cadence sensor, wired together, and magnets for the crank arm and chainstay. ANT+ only but works fine with my XOSS computer. And the entire kits cost me about $10 apiece, including the case for the iPhone, mount, etc. Those are good sensors for only ten bucks, even if you never use the other stuff. I bought two, in 2018 while recovering from injuries, and another in January for a second road bike.

But if your budget stretches to around $50, you can buy some excellent sensors from Garmin or Wahoo.