Yes—older adapted lenses can work well on mirrorless cameras, but there are some common tradeoffs versus modern optics.

Main drawbacks:

• coatings: many older lenses have simpler coatings, so they can be more prone to flare and lower contrast, especially with strong light sources or night scenes.
• transmission/contrast: even if the f-number is the same, some older lenses may transmit light less efficiently and appear less punchy.
• color cast: some vintage lenses can show a yellow tint; this can usually be corrected in post, and certain lenses may clear somewhat with prolonged exposure to sunlight.
• consistency: sample condition matters a lot with older lenses, since age, haze, fungus, or wear can affect results.

Possible upsides:

• character: many people like the rendering and bokeh of vintage lenses, sometimes more than modern lenses.
• adaptability: mirrorless bodies are especially good for using M42 and T-mount lenses because adapting them is straightforward.

So the downside is usually less technical perfection—more flare, lower contrast, possible color tint, and copy-to-copy variation. The upside is distinctive rendering and low cost. If you like the results you’re getting and accept manual focus, there’s no inherent problem using them.