There is no issue with cask aging spirits you legally purchased. The tax has already been paid.
There are some issues. I suspect the casks were made overseas, probably China.
The biggest is leakage. Many casks are not well coopered and have tiny leaks. I put my cask on a stainless tray and spotted leaks immediately. It took two replacement kegs to get one that didn't leak ...much. I never got a valve that didn't leak.
The second place that is a leak problem is the wooden bung valve. Again, cheap manufacture is not tight and won't seal well. I solved that issue by installing a cork in the bung hole. To sample or serve, I tipped the barrel on end and changed to the tap valve, then restored the cork after I was done.
Many of the cheap import casks give you a bar of wax to seal leaks. This is like a manufacturer giving you a box of band-aids to put on cuts instead of fixing a sharp place on an appliance. Some suppliers wax dip the whole cask and buff it for looks. Personally, I don't want to age a good spirit is a waxed cask. Read the feedback on any cask you consider.
On doing some research, I found that it was not recommended to age your spirits more than a year. Some places recommend 8 months. Cask aging is supposedly much faster in a small cask. Cask evaporation is also much faster with most small casks. What I found was that aging a reasonably good spirit for 8 months to a year will mellow it a noticeable amount. It won't turn Cutty Sark into Balvenie or make a 10-year-old single male taste like a 20-year-old ... but there is a detectable improvement.
What I eventually did was find a cask maker in Ukraine that makes a good quality cask in sizes from very small to 1/4 barrel. I'm not sure of his current status.
His casks are much heavier and come charred on the inside and flame darkened on the outside. He will do custom lasering of your name or logo on the end. He has nice extras, like a good cradle with rope accents. His bung valve is much thicker and better than the cheap ones. His barrels cost more but are worth it.
So, what I discovered:
1) Preparation of the cask is of the utmost importance. IT must be washed out with water and then soaked for a full month before use. Use distilled water for soaking and change the water at least twice.
2) Age your spirits six to eight months and enjoy it.
3) Plan ahead for your big summer picnic. Start prepping the cask around November. At Christmas Time, buy enough of your favorite brand to fill the cask (get an extra bottle to keep the cask topped up if needed.). On January 1st, drain the water and fill the cask. Save the bottles for refilling if a serious leak starts.
4) Put the cask on a tray, like a cafeteria tray. This will show you if there are leaks. Check it every week and keep it topped up. If it won't stop leaking, re-bottle te spirtis and ask for a replacement cask.
5) If aging for your own use, re-bottle the spirit after 8 to 12 months.
If put up for a party, re-bottle the spirits not consumed at the event and fill the keg with distilled water. Keep it topped up until you are ready for another party and start the aging process again six months before the party.
6) I have a friend who uses his cask to blend scotch. He mixes a group of spirits that accent each other and casks for them a year. I have tasted his blends and think this works well. But, I suspect if he just bought Vat 69 and cask aged it a year it would be just as good.
Short answer to all this - What the cask does best is look cool! It is a great thing to have on the bar or at a large picnic for guests to tap a wee dram.
Biggest advice - IF YOU WANT a 20-YEAR-OLD SCOTCH OR BOURBON, BUY IT, DON'T TRY AND MAKE IT. I would not recommend putting an expensive spirit in the cask. It will not improve and might end up more oaky.
I had a VIP ticket to the Virginia Invitational Bourbon Tasting held at the Cavalier yesterday. The weather was as perfect as anyone could ask for. There were 15 or so Virginia small still makers there with their new Bourbons, Ryes, Gins, and Vodkas. The event allowed a few of the Kentucky fellows to come, but you couldn't buy their products. Makers Mark has a new Limited Release Wood Finishing Series at 108.4 proof that was outstanding (needs rocks or a little branch water to tame it down).