Both very handy services.
I can buy something with free UK shipping, have it posted to my Parcel Motel or Parcel Wizard UK address and then have it delivered to the ROI for a flat fee of €4 (size/weight restrictions do apply).
Alternatively, if there are UK postage restrictions (e.g. contains alcohol) or the seller only posts to the UK, again PM and PW allow me to avail of same.
When the Royal Mail does work, the UK delivery part is normally made within 2-3 days and PM/PW deliver within 24 hours - so it normally works out quicker too.