Speed is always relative. What is the speed of the current CF card you are using? What is the speed of the microSD card you wish to use? What is the maximum throughput of the SD->CF adapter? In terms of both read and in your case, more importantly, write speed? What is the maximum speed that the camera you are using is capable? The determining factor in the performance of the entire system will be the slowest single element.
In general, the fastest CF cards available at a given time have been faster than the fastest SD cards available at the same time. With the introduction of the UHS-1 standard for SD cards recently, this is less the case than has been in the past. When some of the pro-level DSLRs first introduced dual CF/SD card slots their users soon discovered that the mere presence of a slower SD card in the SD card slot slowed the speed of the read/write operations to the CF card as well, even if they were only writing to the CF card at a particular time.
In your case, the write speed of your camera, the respective speeds of your current CF and SD cards, and the speed of the adapter in question will go a long way in determining if you will take a speed hit by using the microSD card via the SD->CF adapter. Unless you have some very recent SD cards or your CF card(s) is(are) older and/or slower, you will probably see a reduction in write speed. In terms of reliability, the more complex a system is the more opportunity there is for something to fail.