I can only speak about where I live (Scotland, UK). We have clay soil and we pocket planted all of our bare root fruit bushes, hedges, trees, roses etc. We did it in November over 3 years. 100% success rate. We haven't had a single failure.
Slit planting is (as far as I can tell) only ever recommended for hedges. But we do it with everything and it works every time. When we use the conventional approach (digging a big hole, digging in compost and amendments) we tend to get 50% losses.
Learn how to plant barerooted country hedging in our video. Slit planting with weed supression fabric is the best method for all native hedge plants. Buy guaranteed plants and get the best gardening advice at Ashridge Nurseries.
www.ashridgetrees.co.uk