We used to only shop in Lidl for our big shop, then supervalu for mid week milk and the odd few bits. Found we were now spending ~€75 a week in Lidl Vs what used to be ~€50 a week in early 2021 or before.
Moved to doing our big shop in Dunnes but being strict on the vouchers. We either spend just over €50 for €10 off or €75 to use the €5 and €10 vouchers to bring it to €60 (usually 2-3 euro over €60). We've always used a shopping list, but now I keep a mental or phone calculator track of our spend.
We still do a rare Lidl shop for things they do good which are over priced in Dunnes (toilet paper, kitchen paper, ice creams, pasta etc).
The quality of our shop has gone up, but the price is pretty similar. €10 more a month by my expense tracking app. Given the inflation that's happened in the last 6 months since we switched that €10 a month difference is probably negligible.
SAV€R app is also decent enough for finding deals in shops.