How do I find out if this mobile tower is bad for my health?
No, it would not be a good investment. The device you linked to is designed to detect power-line frequencies (50 Hz or 60 Hz). There are more advanced devices, but as the Amazon comments make clear, the demand for them is based on fear and ignorance. The item description refers to "EM pollution" and says that you can use the meter to do "prudent avoidance", but takes it for granted that those are real things. This is clearly designed to scare people into buying a useless (but expensive) product. It's like Monster Cable or those $10,000 oxygen-free speaker wires. 

To emphasize what a joke these detecters are, the other main use for them is ghost hunting. (Seriously. Ghost hunting. Give me a break.)

Meanwhile, here's what the American Cancer Society has to say about cell phone towers and cancer:


  Do cellular phone towers cause cancer?
  
  Some people have expressed concern that living, working, or going to school near a cell phone tower might increase the risk of cancer or other health problems. At this time, there is very little evidence to support this idea. In theory, there are some important points that would argue against cellular phone towers being able to cause cancer.
  
  First, the energy level of radiofrequency (RF) waves is relatively low, especially when compared with the types of radiation that are known to increase cancer risk, such as gamma rays, x-rays, and ultraviolet (UV) light. The energy of RF waves given off by cell phone towers is not enough to break chemical bonds in DNA molecules, which is how these stronger forms of radiation may lead to cancer.
  
  A second issue has to do with wavelength. RF waves have long wavelengths, which can only be concentrated to about an inch or two in size. This makes it unlikely that the energy from RF waves could be concentrated enough to affect individual cells in the body.
  
  Third, even if RF waves were somehow able to affect cells in the body at higher doses, the level of RF waves present at ground level is very low – well below the recommended limits. Levels of energy from RF waves near cell phone towers are not significantly different from the background levels of RF radiation in urban areas from other sources, such as radio and television broadcast stations.
  
  For these reasons, most scientists agree that cell phone antennas or towers are unlikely to cause cancer.


There's also talk about directionality:


  How are people exposed to the energy from cellular phone towers?
  
  As people use cell phones to make calls, signals are transmitted back and forth to the base station. The RF waves produced at the base station are given off into the environment, where people can be exposed to them.
  
  The energy from a cellular phone tower antenna, like that of other telecommunication antennas, is directed toward the horizon (parallel to the ground), with some downward scatter. Base station antennas use higher power levels than other types of land-mobile antennas, but much lower levels than those from radio and television broadcast stations. The amount of energy decreases rapidly as the distance from the antenna increases. As a result, the level of exposure to radio waves at ground level is very low compared to the level close to the antenna.
  
  Public exposure to radio waves from cell phone tower antennas is slight for several reasons. The power levels are relatively low, the antennas are mounted high above ground level, and the signals are transmitted intermittently, rather than constantly.
  
  At ground level near typical cellular base stations, the amount of RF energy is thousands of times less than the limits for safe exposure set by the US Federal Communication Commission (FCC) and other regulatory authorities. It is very unlikely that a person could be exposed to RF levels in excess of these limits just by being near a cell phone tower.
  
  When a cellular antenna is mounted on a roof, it is possible that a person on the roof could be exposed to RF levels greater than those typically encountered on the ground. But even then, exposure levels approaching or exceeding the FCC safety guidelines are only likely to be found very close to and directly in front of the antennas. If this is the case, access to these areas should be limited.
  
  The level of RF energy inside buildings where a base station is mounted is typically much lower than the level outside, depending on the construction materials of the building. Wood or cement block reduces the exposure level of RF radiation by a factor of about 10. The energy level behind an antenna is hundreds to thousands of times lower than in front. Therefore, if an antenna is mounted on the side of a building, the exposure level in the room directly behind the wall is typically well below the recommended exposure limits.


I wouldn't worry about the cell phone tower. If you want to worry about your health, maybe start by looking at the top 10 causes of death in India:


  
  Ischaemic heart disease 12%
  Chronic obstructive pulmonary disease (lung disease) 11%
  Stroke 9%
  Diarrheal disease 6%
  Lower respiratory infections 5%
  Preterm birth complications 4%
  Tuberculosis 3%
  Self-inflicted injuries 3%
  Falls 3%
  Road injury 2%
  


Avoid tobacco smoke, exercise, take care of your mental health, and be careful near roads and ledges. That'll get you a lot farther than worrying about non-ionizing radiation.