Some physician investors absolutely swear by annuities. Others run screaming from them. What kind of investment vehicle could have this polarizing effect on people? Answer: One with great upsides and with equally great downsides.

An annuity is basically an insurance contract. According to Forbes, an annuity will take present contributions from an investor in exchange for future income payments. An annuity can be helpful for adding security to your retirement plan while still maintaining the possibility of market exposure. To that end, there are quite a few options when it comes to annuities and the varying terms can come with varying costs.

One of the best descriptors of annuities comes from AARP, “They’re simple—and complicated.” Keep this in mind when considering them. On the one hand, what could be easier that handing over your money and knowing it will last throughout your retirement? On the other hand, the fees and riders can make the costs of an annuity skyrocket. Plus, the annuity is a big commitment on your part. Once you hand your money over, you are locked in. Here are the basics to bring with you as you explore annuities.

The benefits are tempting. An annuity can offer you predictable payments that may be guaranteed for your lifetime and, depending upon the options you choose, they can last for your spouse’s lifetime as well. There is tax-deferred growth on your investments in an annuity and your payouts are taxed as ordinary income.

There are primarily three types. A fixed annuity guarantees you an annual minimum payment despite the movements of the stock market. With a variable annuity your income depends on market performance, exposing you to a bit more risk. An index annuity also depends on the movements of the market, but it mirrors a specific index like the S&P 500. The caveat is that even these three categories have their variations.

Everything depends on the type of annuity and its riders. It’s all about the details. And then the details on top of the details. Concerns that can be addressed include outliving your income, having income guaranteed for a spouse, protection against inflation, coverage in case of illness, and more. Make sure these are all clearly explained in writing.

Work with someone you trust. Because annuities can mean big commissions for the person selling them, work with a financial advisor that you have a good relationship with. Also make sure that your specific needs and goals are met—which could mean not wanting to use an annuity at all.