I bought Daystar Quark Prominence and a Baader UV-IR cut filter for my 70 mm ED F/6 refractor. My eyepiece is a 32 mm Svbony Plossl.
I plugged the Quark, left it on its default tuning position ("12 o'clock") and waited for it to heat up (about 15 minutes). It was 24C (75F) outside.
I was completely stunned by the view at the eyepiece.
A generous full disk view (amber-bright red hue), prominences and spicules were obvious, generous details on them. The disk was rich in details, several filaments, complex patterns around and between sunspots, plus granulation everywhere. I even caught a flare forming in real time.
I was stuck to the eyepiece for one hour, watching prominences slowly evolve (their changes are visible after 15 minutes). It's an unforgettable experience.
Remember that you have 2 variables to play with : focus and tuning.
I live under jet stream, so I'm under lots of atmospheric turbulence.
Focus must often be adjusted, same as night time astronomy.
Tuning is not so obvious because it depends on temperature.
The day after, it was a bit hotter outside (27C, 80F), and noticed that the optimal position was at "11 o'clock".
Note that everytime you adjust tuning, you must wait another 10-15 minutes for the green light.
After that, I got a cooler session at 21C (70F) and realized the best
position was at "1 o'clock". You have to be patient and experiment.
The optimal tuning is obvious : it's where you get the most detailed view of the solar disk. If the Sun turns into a red dull disk, you went too far to one side or the other.
According to DayStar Quark documentation, I didn't need an UV-IR cut filter for a 70 mm refractor for short sessions. However, I knew I was going to be stuck for long sessions and preferred not to play with my eyesight. Better be safe and add the UV-IR cut filter.
Note that larger telescopes may need an ERF (front) filter.
In a few words : I strongly recommend it.