I had a few mid era Epos speakers, including the M5i as well as their larger brothers the 12.2. Unfortunately, from my perspective, not the most 'musical' speakers. More a clinical HiFi sound. - None lasted long in my systems. - Very good build though. The exception were Mordaunt Shorts MS10i and MS20i Pearls. Fantastic speakers borrowing heavily from Marshall's original designs but made for a lower price point. IMHO better than any of EPOS's mid era offerings.
£100 is not a lot for speakers, even 2nd hand and you can't expect too much. The best you can hope for is that what they do is reasonable and that they don't attempt to chew off too much. Aside of the afromentioned Pearl's two speakers stand out for me; Mission's M71i (an improved version from the one reviewed, measured and recommended by Stereophile) and, at a little more than your budget, perhaps £150 - £200, Usher's terrific little S520 which sound and look far better than the original RRP. A mini monitor in the true sense. - By the way Mission even made a dedicated stand for the M71.
None of those sound the same but are my pick for cheap speakers.
With a Brio, I'd probably try the Mission's or Pearls, both easy to drive and forgiving. The Usher ideally requires more powerful amplification but have more scope for upgrades down the line.