This tends to be a common approach for hot tubs becuase it offers strong support for the weight and also keeps the area nice and clean. Concrete is solid, not overly expensive and is quite easy to lay. If you are worried about how it will look then simply make the pad slighty bigger than the footprint of the hot tub and this will hide the 'concrete' look. You can also add a deck or patio trim around the bottom if there is visible concrete that you find unsightly.
We recommend a concrete pad that is at least 10cm thick. We also recommend the concrete to be sloped at 1.5cm per 3.5m, this ensures water runs off the pad and prevents pooling.
Most patios, block paving and other surfaces are already reinforced and will be able to take the weight of a hot tub placement. If you are unsure then you may need to consult a specialist in this area. The benefit of using an existing area is of course cost saving but there is also a time consideration as less preperation is required. It is worth ensuring the stones are level and also worth ensuring the drainage is ok as you do not want water to pool under the hot tub.
Decking is a very popular option for a couple of reasons in our opinion. It looks great and it is nice underfoot when getting in and out the outdoor hot tub. One drawback to using decking is longevity as most decking has a short lifespan however with new composites on the market this is less of an issue.
If you are looking to install a hot tub on decking then you must consider the strength of the support underneath and consult a specialist decking installer. You need more joists to support a hot tub than on a normal deck and you will need to ensure the foundations below are sufficient, whether this is concrete or another type of hardcode.
Having read the above you will realise the positives and negatives of certain surfaces and some of the factors that you need to consider. As a general rule, as long as drainage is good, the surface is relativley flat, solid and will take the weight of a full hot tub then it should be absolutley fine.